Rancher 2.6

Ondat with Rancher by SUSE #

A Kubernetes-native data plane for critical workloads

Technical Reference Documentation

Getting Started

Authors

Rodney Karemba, Solutions Architect (Ondat)

Andy King, Alliances Solutions Architect (SUSE)

Terry Smith, Global Partner Solutions Director (SUSE)

Rancher by SUSE

Date: 2023-01-11

Summary

This document provides a brief introduction to Ondat with Rancher by SUSE for Kubernetes-native storage for critical workloads, such as Database-as-a-Service.

SUSE One Partner Solution Stacks are featured, SUSE-confirmed solutions, collaboratively developed with SUSE and partner components and designed to arm organizations with the capabilities and agility they need to achieve success.

Disclaimer

Documents published as part of the series SUSE Technical Reference Documentation have been contributed voluntarily by SUSE employees and third parties. They are meant to serve as examples of how particular actions can be performed. They have been compiled with utmost attention to detail. However, this does not guarantee complete accuracy. SUSE cannot verify that actions described in these documents do what is claimed or whether actions described have unintended consequences. SUSE LLC, its affiliates, the authors, and the translators may not be held liable for possible errors or the consequences thereof.

1 Introduction #

1.1 Motivation #

The design of your cloud native Kubernetes environment requires several critical selections to meet operational, performance, flexibility, resilience, and security needs.

Rancher by SUSE is often the multi-cluster Kubernetes management platform of choice, unifying your cloud native application landscape to ensure consistent, streamlined operations and enterprise-grade security from core to cloud to edge.

Another serious consideration is the selection of a persistent storage solution for your cloud native application data. Ondat is a Kubernetes-native, persistent storage platform, designed to deliver high performance, guaranteed high availability, and security for all your critical workloads. Like Rancher by SUSE, Ondat is cloud platform agnostic, allowing you to free your data whilst significantly reducing your cloud storage operational costs for stateful applications.

SUSE and Ondat provide you with a complete cloud and Kubernetes-native technical stack that does not compromise on the key features modern developers and businesses expect in today’s data-driven environment.

Key features include:

Data replication and high availability
Leverage resilient storage with automatic failover and healing to ensure uninterrupted access to your data.
High performance
Get top performance with low latency access to data for stateful applications enabling you to run your own databases (such as Database-as-a-Service or DBaaS) and other stateful applications in your Kubernetes clusters.
Security
Secure your application data with encryption at rest and in transit on a per volume basis.
Scalability
Scale your storage horizontally by adding more cluster nodes or vertically by adding more capacity to existing nodes.
Platform freedom
Escape infrastructure lock-in with support for all CNCF-certified Kubernetes distributions and cloud platforms.

1.2 Scope #

This guide walks through the basic steps for deploying Ondat with Rancher 2.6 and demonstrates the high availability use case with a stateful application.

1.3 Audience #

This document is intended for DevOps engineers, site reliability engineers (SREs), platform engineers, software engineers, and developers who are responsible for managing and running stateful workloads in Kubernetes clusters.

2 Technical overview #

Ondat uses storage attached to the Kubernetes cluster nodes to create and present persistent, virtual volumes into containers. Ondat is designed to feel familiar to Kubernetes users: storage is managed through standard StorageClasses and PersistentVolumeClaims, and features are controlled by native Kubernetes Labels and selectors, prefixed with storageos.com/. Caching is enabled by default to improve read performance and compressed to reduced network traffic.

Core Ondat components are:

Ondat Cluster Operator
Creates and maintains the Ondat storage cluster by ensuring all relevant components are running.
Ondat Controlplane
Monitors and maintains the state of volumes and nodes, working with etcd to maintain state consensus.
Ondat Dataplane
Handles all I/O path related tasks, including reading, writing, compression, and caching.
Ondat Scheduler
Helps ensure applications are scheduled on the same node as their volumes.
CSI Helper
Registers Ondat with Kubernetes as a CSI driver, creating and deleting volumes in response to PersistentVolumeClaims.
Ondat API Manager
Facilitates communication between various APIs and the Ondat Controlplane API. It continually monitors the state of the cluster and moves it toward the desired state as necessary.

3 Prerequisites #

Ensure that you have checked that the following prerequisites have been met before proceeding to the next section.

Kubernetes cluster with at least 3 worker nodes.
Review Ondat prerequisites for more on minimal and recommended resource requirements.
Note
This guide uses a Rancher 2.6 environment with an RKE v1.20.15 cluster consisting of 3 master nodes and 5 worker nodes.
Sufficient Role-Based Access Control (RBAC) permissions to deploy and manage applications in the cluster.
For more guidance, see the Rancher documentation.
Block storage available on each worker node. Ondat will use these to create a single storage pool for storing persistent data.
The following LinuxIO kernel modules loaded on the worker nodes:
- target_core_mod
- tcm_loop
- target_core_file
- configfs
- target_core_user
- uio
Essential CLI utilities
Ensure these CLI utilities are installed on your local machine and are available in your $PATH:
- kubectl
- kubectl-storageos

4 Installation #

Installing Ondat into your Kubernetes cluster with Rancher 2.6 is easy. The two recommended methods are:

Through Rancher Apps catalog using the Ondat Operator Partner Chart.
With the Ondat kubectl plug-in.

In this guide, you use the Ondat kubectl plug-in to install Ondat and deploy an etcd cluster operator in your Kubernetes cluster with Rancher 2.6.

Install local path provisioner.
By default, a newly provisioned Kubernetes cluster does not have a deployed CSI driver.
Run the following commands against the cluster to deploy a Local Path Provisioner to provide local storage for an etcd cluster.
Note
The Local Path Provisioner stores all data locally on the individual nodes and is not recommended for production installations.
```
# Install the local path provisioner.
kubectl apply --filename="https://raw.githubusercontent.com/rancher/local-path-provisioner/v0.0.21/deploy/local-path-storage.yaml"

# Inspect the status of the pod and storageclass.
kubectl get pod --namespace=local-path-storage
kubectl get storageclass
```
Conduct preflight checks.
Run the following kubectl-storageos plug-in command to conduct preflight checks against the Kubernetes cluster to validate that key Ondat prerequisites have been met before proceeding.
```
# Conduct preflight checks.
kubectl storageos preflight
```
Create your Ondat credentials.
Define and export the STORAGEOS_USERNAME and STORAGEOS_PASSWORD environment variables that will be used as your credentials to access and manage your Ondat instance.
```
export STORAGEOS_USERNAME="admin"
export STORAGEOS_PASSWORD="password"
```

Install Ondat.

Run the following kubectl-storageos plug-in command to install Ondat.

# Install Ondat.
kubectl storageos install \
  --include-etcd \
  --etcd-tls-enabled \
  --etcd-storage-class="local-path" \
  --admin-username="$STORAGEOS_USERNAME" \
  --admin-password="$STORAGEOS_PASSWORD"

Note

The installation process may take a few minutes.

Verify the Ondat installation.
When the installation is complete, inspect Ondat’s resources. The core components should all show a status of RUNNING.
```
# Inspect Ondat resources that have been created.
kubectl get all --namespace=storageos
kubectl get all --namespace=storageos-etcd
kubectl get storageclasses | grep "storageos"
```
You can also review the status of the components in the Rancher 2.6 Management Server UI.
Apply a licence to the cluster.
Newly installed Ondat clusters will run unlicensed for 24 hours without any limitations. Thereafter, the Ondat cluster must be licensed to ensure that new operations, such as volume provisioning or adding nodes, continue to work.
Review the licensing overview to learn about Ondat licensing, including free options.

5 Configuration #

After Ondat is installed and running, you need to create a custom Ondat StorageClass and configure it as the default for your cluster to enable these key features:

[Replication](https://docs.ondat.io/docs/concepts/replication/)
[Topology-Aware Placement (TAP)](https://docs.ondat.io/docs/operations/tap/)
[Encryption](https://docs.ondat.io/docs/reference/encryption/)

Follow the steps below to configure your Ondat cluster.

Define custom region feature labels for the nodes in the cluster.

# Label the worker nodes to define custom regions for the TAP feature.
kubectl label node demo-worker-node-1 custom-region=1
kubectl label node demo-worker-node-2 custom-region=2
kubectl label node demo-worker-node-3 custom-region=3
kubectl label node demo-worker-node-4 custom-region=1
kubectl label node demo-worker-node-5 custom-region=2

# Check that the worker nodes have been labeled successfully.
kubectl describe nodes | grep "custom-region"

Create a custom Ondat StorageClass, named ondat-replication.

# Create the Ondat StorageClass.
cat <<EOF | kubectl create --filename -
apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: ondat-replication
provisioner: csi.storageos.com
allowVolumeExpansion: true
parameters:
  csi.storage.k8s.io/fstype: ext4
  storageos.com/replicas: "2"
  storageos.com/topology-aware: "true"
  storageos.com/topology-key: "custom-region"
  csi.storage.k8s.io/secret-name: storageos-api
  csi.storage.k8s.io/secret-namespace: storageos
EOF

Mark the custom Ondat StorageClass as default for the cluster.

# Set as default.
kubectl patch storageclass ondat-replication -p '{"metadata": {"annotations":{"storageclass.kubernetes.io/is-default-class":"true"}}}'

# Inspect the StorageClass and ensure it's now the default.
kubectl get storageclasses | grep "ondat-replication"

You can also review the custom Ondat StorageClass through the Rancher 2.6 Management Server UI.

rancher ondat server ui custom ondat storageclass

Your Ondat cluster is now configured.

Before proceeding to the demonstration, follow the steps below to deploy and run the Ondat CLI utility as a deployment so that you can interact and manage Ondat through kubectl.

Deploy the CLI utility in the storageos namespace.

# Create the deployment for the Ondat CLI.
cat <<EOF | kubectl create --filename -
apiVersion: apps/v1
kind: Deployment
metadata:
  name: storageos-cli
  namespace: storageos
  labels:
    app: storageos
    run: cli
spec:
  replicas: 1
  selector:
    matchLabels:
      app: storageos-cli
      run: cli
  template:
    metadata:
      labels:
        app: storageos-cli
        run: cli
    spec:
      containers:
      - command:
        - /bin/sh
        - -c
        - "while true; do sleep 3600; done"
        env:
        - name: STORAGEOS_ENDPOINTS
          value: http://storageos:5705
        - name: STORAGEOS_USERNAME
          value: "admin"
        - name: STORAGEOS_PASSWORD
          value: "password"
        image: storageos/cli:v2.5.0
        name: cli
EOF

Obtain the CLI utility pod name for later reference.

# Get the CLI utility pod name.
kubectl --namespace=storageos get pod -ocustom-columns=_:.metadata.name --no-headers -lapp=storageos-cli

storageos-cli-77748d9c84-dtbg7

6 Demonstration #

Next, you explore how Ondat with Rancher by SUSE helps ensure that stateful workload data are always highly available by:

deploying a stateful application that leverages the ondat-replication StorageClass created earlier.
simulating a node failure scenario to demonstrate how Ondat’s replication feature can quickly fail over to a new replica volume when a master volume suddenly goes permanently offline.

6.1 Deploy a stateful application #

For this demonstration, you will deploy MongoDB as the stateful application, using the MongoDB operator developed and maintained by Percona.

Deploy the operator with kubectl.

# Create a namespace for the operator.
kubectl create namespace mongodb

# Deploy the MongoDB operator.
kubectl --namespace=mongodb apply --filename="https://raw.githubusercontent.com/percona/percona-server-mongodb-operator/v1.11.0/deploy/bundle.yaml"

# Inspect that the status of the pod is in a `Running` state.
kubectl get pods --namespace=mongodb

After the operator is ready, create the database cluster itself from the example cr-minimal.yaml custom resource located in the MongoDB operator repository.

# Deploy the database cluster.
kubectl --namespace=mongodb apply --filename="https://raw.githubusercontent.com/percona/percona-server-mongodb-operator/v1.11.0/deploy/cr-minimal.yaml"

# Inspect and wait until that the resources have been successfully created in the `mongodb` namespace.
kubectl get pods --namespace=mongodb

When the database is running, you should see that Ondat automatically created two replica volumes for each master volume. Verify this with the following command:

# Get the volumes in the `mongodb` namespace using `kubectl`
kubectl get pvc --namespace=mongodb

NAME                                STATUS   VOLUME                                     CAPACITY   ACCESS MODES   STORAGECLASS        AGE
mongod-data-minimal-cluster-cfg-0   Bound    pvc-e875c38a-0d86-4851-9a65-5e1f6c6b811b   3Gi        RWO            ondat-replication   4m35s
mongod-data-minimal-cluster-rs0-0   Bound    pvc-9af262b3-ab50-4d68-87bc-60eb825f1f99   3Gi        RWO            ondat-replication   4m35s

# Get the volumes in the `mongodb` namespace using the Ondat CLI.
kubectl --namespace=storageos exec storageos-cli-77748d9c84-dtbg7 -- storageos get volumes --namespace=mongodb

NAMESPACE  NAME                                      SIZE     LOCATION                     ATTACHED ON         REPLICAS  AGE
mongodb    pvc-e875c38a-0d86-4851-9a65-5e1f6c6b811b  3.0 GiB  demo-worker-node-2 (online)  demo-worker-node-2  2/2       5 minutes ago
mongodb    pvc-9af262b3-ab50-4d68-87bc-60eb825f1f99  3.0 GiB  demo-worker-node-2 (online)  demo-worker-node-2  2/2       5 minutes ago

# Describe the `pvc-9af262b3-ab50-4d68-87bc-60eb825f1f99` volume.
kubectl --namespace=storageos exec storageos-cli-77748d9c84-dtbg7 -- storageos describe volume pvc-9af262b3-ab50-4d68-87bc-60eb825f1f99 --namespace=mongodb

ID                  d4f7d463-1bf3-4521-b248-0e9ebe1143a0
Name                pvc-9af262b3-ab50-4d68-87bc-60eb825f1f99
Description
AttachedOn          demo-worker-node-2 (0b61b84d-7b35-4b55-80ee-b65b92f65e0d)
Attachment Type     host
NFS
  Service Endpoint
  Exports:
Namespace           mongodb (54f0f4cc-c6a3-48d0-aa64-446cde6ac288)
Labels              app.kubernetes.io/component=mongod,
                    app.kubernetes.io/instance=minimal-cluster,
                    app.kubernetes.io/managed-by=percona-server-mongodb-operator,
                    app.kubernetes.io/name=percona-server-mongodb,
                    app.kubernetes.io/part-of=percona-server-mongodb,
                    app.kubernetes.io/replset=rs0,
                    csi.storage.k8s.io/pv/name=pvc-9af262b3-ab50-4d68-87bc-60eb825f1f99,
                    csi.storage.k8s.io/pvc/name=mongod-data-minimal-cluster-rs0-0,
                    csi.storage.k8s.io/pvc/namespace=mongodb,
                    storageos.com/nocompress=true,
                    storageos.com/replicas=2,
                    storageos.com/topology-aware=true,
                    storageos.com/topology-key=custom-region
Filesystem          ext4
Size                3.0 GiB (3221225472 bytes)
Version             Mw
Created at          2022-03-23T12:55:31Z (8 minutes ago)
Updated at          2022-03-23T12:55:37Z (7 minutes ago)

Master:
  ID                961c827c-6b00-4e36-972d-2d187ec3729f
  Node              demo-worker-node-2 (0b61b84d-7b35-4b55-80ee-b65b92f65e0d)
  Health            online
  Topology Domain   2

Replicas:
  ID                371cc374-9644-4b21-ae4b-ae640a2601b7
  Node              demo-worker-node-1 (50071bba-e908-4cf0-ad5c-1e62096a9ecf)
  Health            ready
  Promotable        true
  Topology Domain   1

  ID                cd0ee062-9369-4639-9ed7-2cfbdf4a4ab2
  Node              demo-worker-node-3 (707f17cb-67af-447a-87de-73832c2945ee)
  Health            ready
  Promotable        true
  Topology Domain   3

As shown in this output, the master volume and each replica volume are deployed on a different nodes to ensure data protection and high availability in the event of a transient node failure. This is the TAP feature in action, which is leveraging the custom regions node labels that were created earlier.

6.2 Simulate a node failure #

Ondat automatically fails over to a replica volume on a different node in the event of a sudden node outage. To see this, you will purposefully delete the node hosting the stateful application’s master volume.

From the output of the previous command, you know that the master volume resides on demo-worker-node-2 and the related replica volumes reside on demo-worker-node-1 and demo-worker-node-3.

When demo-worker-node-2 goes offline, Ondat automatically detects that the master volume no longer exists. Then it elects one of the replicas to become a master and creates a new replica on a different node to maintain the defined replica volume count.

Note

The nodes where the volumes reside may be different for your cluster. Ensure that you substitute the correct node names in the commands below.

Delete demo-worker-node-2 (containing the master volume).

# Delete the node with a master volume.
kubectl delete node/demo-worker-node-2

# Check that the node has been successfully deleted.
kubectl get nodes

NAME                 STATUS   ROLES               AGE     VERSION
demo-master-node-1   Ready    controlplane,etcd   3h5m    v1.20.15
demo-master-node-2   Ready    controlplane,etcd   3h6m    v1.20.15
demo-master-node-3   Ready    controlplane,etcd   3h12m   v1.20.15
demo-worker-node-1   Ready    worker              3h4m    v1.20.15
demo-worker-node-3   Ready    worker              3h4m    v1.20.15
demo-worker-node-4   Ready    worker              3h4m    v1.20.15
demo-worker-node-5   Ready    worker              3h11m   v1.20.15

Wait a couple minutes, then review the volumes again.

kubectl --namespace=storageos exec storageos-cli-77748d9c84-dtbg7 -- storageos get volumes --namespace=mongodb

NAMESPACE  NAME                                      SIZE     LOCATION                     ATTACHED ON  REPLICAS  AGE
mongodb    pvc-e875c38a-0d86-4851-9a65-5e1f6c6b811b  3.0 GiB  demo-worker-node-1 (online)               2/2       24 minutes ago
mongodb    pvc-9af262b3-ab50-4d68-87bc-60eb825f1f99  3.0 GiB  demo-worker-node-3 (online)               2/2       24 minutes ago

# Get the volumes in the `mongodb` namespace using `kubectl`
kubectl get pvc --namespace=mongodb

NAME                                STATUS   VOLUME                                     CAPACITY   ACCESS MODES   STORAGECLASS        AGE
mongod-data-minimal-cluster-cfg-0   Bound    pvc-e875c38a-0d86-4851-9a65-5e1f6c6b811b   3Gi        RWO            ondat-replication   25m
mongod-data-minimal-cluster-rs0-0   Bound    pvc-9af262b3-ab50-4d68-87bc-60eb825f1f99   3Gi        RWO            ondat-replication   25m

# Describe the volume `pvc-9af262b3-ab50-4d68-87bc-60eb825f1f99`.
kubectl --namespace=storageos exec storageos-cli-77748d9c84-dtbg7 -- storageos describe volume pvc-9af262b3-ab50-4d68-87bc-60eb825f1f99 --namespace=mongodb

ID                  d4f7d463-1bf3-4521-b248-0e9ebe1143a0
Name                pvc-9af262b3-ab50-4d68-87bc-60eb825f1f99
Description
AttachedOn          demo-worker-node-1 (50071bba-e908-4cf0-ad5c-1e62096a9ecf)
Attachment Type     host
NFS
  Service Endpoint
  Exports:
Namespace           mongodb (54f0f4cc-c6a3-48d0-aa64-446cde6ac288)
Labels              app.kubernetes.io/component=mongod,
                    app.kubernetes.io/instance=minimal-cluster,
                    app.kubernetes.io/managed-by=percona-server-mongodb-operator,
                    app.kubernetes.io/name=percona-server-mongodb,
                    app.kubernetes.io/part-of=percona-server-mongodb,
                    app.kubernetes.io/replset=rs0,
                    csi.storage.k8s.io/pv/name=pvc-9af262b3-ab50-4d68-87bc-60eb825f1f99,
                    csi.storage.k8s.io/pvc/name=mongod-data-minimal-cluster-rs0-0,
                    csi.storage.k8s.io/pvc/namespace=mongodb,
                    storageos.com/nocompress=true,
                    storageos.com/replicas=2,
                    storageos.com/topology-aware=true,
                    storageos.com/topology-key=custom-region
Filesystem          ext4
Size                3.0 GiB (3221225472 bytes)
Version             OQ
Created at          2022-03-23T12:55:31Z (45 minutes ago)
Updated at          2022-03-23T13:21:54Z (19 minutes ago)

Master:
  ID                cd0ee062-9369-4639-9ed7-2cfbdf4a4ab2
  Node              demo-worker-node-3 (707f17cb-67af-447a-87de-73832c2945ee)
  Health            online
  Topology Domain   3

Replicas:
  ID                371cc374-9644-4b21-ae4b-ae640a2601b7
  Node              demo-worker-node-1 (50071bba-e908-4cf0-ad5c-1e62096a9ecf)
  Health            ready
  Promotable        true
  Topology Domain   1

  ID                0322ffc6-49b0-458a-a08b-44ebdd8f152c
  Node              demo-worker-node-5 (0c62c0c2-871d-4289-87c4-509d9edfff0c)
  Health            ready
  Promotable        true
  Topology Domain   2

# Check the status of the pods running in `mongodb` and wait until
# they have been successfully initialised and are in a `Running` state.
kubectl get pods --namespace=mongodb

NAME                                               READY   STATUS    RESTARTS   AGE
minimal-cluster-cfg-0                              1/1     Running   0          28m
minimal-cluster-mongos-6d57dc7cd-zzdwz             1/1     Running   2          49m
minimal-cluster-rs0-0                              1/1     Running   0          28m
percona-server-mongodb-operator-5dd88ff7f7-ncqcn   1/1     Running   0          51m

In this example output, notice that Ondat elected the replica volume on demo-worker-node-3 to host the master volume since demo-worker-node-2 no longer exists. Also notice that a new replica volume was automatically created on demo-worker-node-5 to ensure that the replica count remains at two, as defined.

7 Summary #

In this guide, you:

deployed Ondat into a Kubernetes cluster in your Rancher 2.6 landscape.
created a custom StorageClass, which enabled replication and Topology-Aware Placement (TAP) to guarantee two replica volumes distributed on nodes in different availability zones.
demonstrated how Ondat can automatically detect an offline master volume, elect a replica volume to become master, and create a new replica on a different node to maintain the defined configuration.

With Ondat and Rancher by SUSE, you can create a Kubernetes-native stack that ensures your critical, stateful workloads are highly available and durable.

8 Additional resources #

9 Legal notice #

Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or (at your option) version 1.3; with the Invariant Section being this copyright notice and license. A copy of the license version 1.2 is included in the section entitled "GNU Free Documentation License".

SUSE, the SUSE logo and YaST are registered trademarks of SUSE LLC in the United States and other countries. For SUSE trademarks, see https://www.suse.com/company/legal/.

Linux is a registered trademark of Linus Torvalds. All other names or trademarks mentioned in this document may be trademarks or registered trademarks of their respective owners.

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Copyright © 2000, 2001, 2002 Free Software Foundation, Inc. 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. Everyone is permitted to copy and distribute verbatim copies of this license document, but changing it is not allowed.

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A "Transparent" copy of the Document means a machine-readable copy, represented in a format whose specification is available to the general public, that is suitable for revising the document straightforwardly with generic text editors or (for images composed of pixels) generic paint programs or (for drawings) some widely available drawing editor, and that is suitable for input to text formatters or for automatic translation to a variety of formats suitable for input to text formatters. A copy made in an otherwise Transparent file format whose markup, or absence of markup, has been arranged to thwart or discourage subsequent modification by readers is not Transparent. An image format is not Transparent if used for any substantial amount of text. A copy that is not "Transparent" is called "Opaque".

Examples of suitable formats for Transparent copies include plain ASCII without markup, Texinfo input format, LaTeX input format, SGML or XML using a publicly available DTD, and standard-conforming simple HTML, PostScript or PDF designed for human modification. Examples of transparent image formats include PNG, XCF and JPG. Opaque formats include proprietary formats that can be read and edited only by proprietary word processors, SGML or XML for which the DTD and/or processing tools are not generally available, and the machine-generated HTML, PostScript or PDF produced by some word processors for output purposes only.

The "Title Page" means, for a printed book, the title page itself, plus such following pages as are needed to hold, legibly, the material this License requires to appear in the title page. For works in formats which do not have any title page as such, "Title Page" means the text near the most prominent appearance of the work’s title, preceding the beginning of the body of the text.

A section "Entitled XYZ" means a named subunit of the Document whose title either is precisely XYZ or contains XYZ in parentheses following text that translates XYZ in another language. (Here XYZ stands for a specific section name mentioned below, such as "Acknowledgements", "Dedications", "Endorsements", or "History".) To "Preserve the Title" of such a section when you modify the Document means that it remains a section "Entitled XYZ" according to this definition.

The Document may include Warranty Disclaimers next to the notice which states that this License applies to the Document. These Warranty Disclaimers are considered to be included by reference in this License, but only as regards disclaiming warranties: any other implication that these Warranty Disclaimers may have is void and has no effect on the meaning of this License.

2. VERBATIM COPYING#

You may copy and distribute the Document in any medium, either commercially or noncommercially, provided that this License, the copyright notices, and the license notice saying this License applies to the Document are reproduced in all copies, and that you add no other conditions whatsoever to those of this License. You may not use technical measures to obstruct or control the reading or further copying of the copies you make or distribute. However, you may accept compensation in exchange for copies. If you distribute a large enough number of copies you must also follow the conditions in section 3.

You may also lend copies, under the same conditions stated above, and you may publicly display copies.

3. COPYING IN QUANTITY#

If you publish printed copies (or copies in media that commonly have printed covers) of the Document, numbering more than 100, and the Document’s license notice requires Cover Texts, you must enclose the copies in covers that carry, clearly and legibly, all these Cover Texts: Front-Cover Texts on the front cover, and Back-Cover Texts on the back cover. Both covers must also clearly and legibly identify you as the publisher of these copies. The front cover must present the full title with all words of the title equally prominent and visible. You may add other material on the covers in addition. Copying with changes limited to the covers, as long as they preserve the title of the Document and satisfy these conditions, can be treated as verbatim copying in other respects.

If the required texts for either cover are too voluminous to fit legibly, you should put the first ones listed (as many as fit reasonably) on the actual cover, and continue the rest onto adjacent pages.

If you publish or distribute Opaque copies of the Document numbering more than 100, you must either include a machine-readable Transparent copy along with each Opaque copy, or state in or with each Opaque copy a computer-network location from which the general network-using public has access to download using public-standard network protocols a complete Transparent copy of the Document, free of added material. If you use the latter option, you must take reasonably prudent steps, when you begin distribution of Opaque copies in quantity, to ensure that this Transparent copy will remain thus accessible at the stated location until at least one year after the last time you distribute an Opaque copy (directly or through your agents or retailers) of that edition to the public.

It is requested, but not required, that you contact the authors of the Document well before redistributing any large number of copies, to give them a chance to provide you with an updated version of the Document.

4. MODIFICATIONS#

You may copy and distribute a Modified Version of the Document under the conditions of sections 2 and 3 above, provided that you release the Modified Version under precisely this License, with the Modified Version filling the role of the Document, thus licensing distribution and modification of the Modified Version to whoever possesses a copy of it. In addition, you must do these things in the Modified Version:

Use in the Title Page (and on the covers, if any) a title distinct from that of the Document, and from those of previous versions (which should, if there were any, be listed in the History section of the Document). You may use the same title as a previous version if the original publisher of that version gives permission.
List on the Title Page, as authors, one or more persons or entities responsible for authorship of the modifications in the Modified Version, together with at least five of the principal authors of the Document (all of its principal authors, if it has fewer than five), unless they release you from this requirement.
State on the Title page the name of the publisher of the Modified Version, as the publisher.
Preserve all the copyright notices of the Document.
Add an appropriate copyright notice for your modifications adjacent to the other copyright notices.
Include, immediately after the copyright notices, a license notice giving the public permission to use the Modified Version under the terms of this License, in the form shown in the Addendum below.
Preserve in that license notice the full lists of Invariant Sections and required Cover Texts given in the Document’s license notice.
Include an unaltered copy of this License.
Preserve the section Entitled "History", Preserve its Title, and add to it an item stating at least the title, year, new authors, and publisher of the Modified Version as given on the Title Page. If there is no section Entitled "History" in the Document, create one stating the title, year, authors, and publisher of the Document as given on its Title Page, then add an item describing the Modified Version as stated in the previous sentence.
Preserve the network location, if any, given in the Document for public access to a Transparent copy of the Document, and likewise the network locations given in the Document for previous versions it was based on. These may be placed in the "History" section. You may omit a network location for a work that was published at least four years before the Document itself, or if the original publisher of the version it refers to gives permission.
For any section Entitled "Acknowledgements" or "Dedications", Preserve the Title of the section, and preserve in the section all the substance and tone of each of the contributor acknowledgements and/or dedications given therein.
Preserve all the Invariant Sections of the Document, unaltered in their text and in their titles. Section numbers or the equivalent are not considered part of the section titles.
Delete any section Entitled "Endorsements". Such a section may not be included in the Modified Version.
Do not retitle any existing section to be Entitled "Endorsements" or to conflict in title with any Invariant Section.
Preserve any Warranty Disclaimers.

If the Modified Version includes new front-matter sections or appendices that qualify as Secondary Sections and contain no material copied from the Document, you may at your option designate some or all of these sections as invariant. To do this, add their titles to the list of Invariant Sections in the Modified Version’s license notice. These titles must be distinct from any other section titles.

You may add a section Entitled "Endorsements", provided it contains nothing but endorsements of your Modified Version by various parties—for example, statements of peer review or that the text has been approved by an organization as the authoritative definition of a standard.

You may add a passage of up to five words as a Front-Cover Text, and a passage of up to 25 words as a Back-Cover Text, to the end of the list of Cover Texts in the Modified Version. Only one passage of Front-Cover Text and one of Back-Cover Text may be added by (or through arrangements made by) any one entity. If the Document already includes a cover text for the same cover, previously added by you or by arrangement made by the same entity you are acting on behalf of, you may not add another; but you may replace the old one, on explicit permission from the previous publisher that added the old one.

The author(s) and publisher(s) of the Document do not by this License give permission to use their names for publicity for or to assert or imply endorsement of any Modified Version.

5. COMBINING DOCUMENTS#

You may combine the Document with other documents released under this License, under the terms defined in section 4 above for modified versions, provided that you include in the combination all of the Invariant Sections of all of the original documents, unmodified, and list them all as Invariant Sections of your combined work in its license notice, and that you preserve all their Warranty Disclaimers.

The combined work need only contain one copy of this License, and multiple identical Invariant Sections may be replaced with a single copy. If there are multiple Invariant Sections with the same name but different contents, make the title of each such section unique by adding at the end of it, in parentheses, the name of the original author or publisher of that section if known, or else a unique number. Make the same adjustment to the section titles in the list of Invariant Sections in the license notice of the combined work.

In the combination, you must combine any sections Entitled "History" in the various original documents, forming one section Entitled "History"; likewise combine any sections Entitled "Acknowledgements", and any sections Entitled "Dedications". You must delete all sections Entitled "Endorsements".

6. COLLECTIONS OF DOCUMENTS#

You may make a collection consisting of the Document and other documents released under this License, and replace the individual copies of this License in the various documents with a single copy that is included in the collection, provided that you follow the rules of this License for verbatim copying of each of the documents in all other respects.

You may extract a single document from such a collection, and distribute it individually under this License, provided you insert a copy of this License into the extracted document, and follow this License in all other respects regarding verbatim copying of that document.

7. AGGREGATION WITH INDEPENDENT WORKS#

A compilation of the Document or its derivatives with other separate and independent documents or works, in or on a volume of a storage or distribution medium, is called an "aggregate" if the copyright resulting from the compilation is not used to limit the legal rights of the compilation’s users beyond what the individual works permit. When the Document is included in an aggregate, this License does not apply to the other works in the aggregate which are not themselves derivative works of the Document.

If the Cover Text requirement of section 3 is applicable to these copies of the Document, then if the Document is less than one half of the entire aggregate, the Document’s Cover Texts may be placed on covers that bracket the Document within the aggregate, or the electronic equivalent of covers if the Document is in electronic form. Otherwise they must appear on printed covers that bracket the whole aggregate.

8. TRANSLATION#

Translation is considered a kind of modification, so you may distribute translations of the Document under the terms of section 4. Replacing Invariant Sections with translations requires special permission from their copyright holders, but you may include translations of some or all Invariant Sections in addition to the original versions of these Invariant Sections. You may include a translation of this License, and all the license notices in the Document, and any Warranty Disclaimers, provided that you also include the original English version of this License and the original versions of those notices and disclaimers. In case of a disagreement between the translation and the original version of this License or a notice or disclaimer, the original version will prevail.

If a section in the Document is Entitled "Acknowledgements", "Dedications", or "History", the requirement (section 4) to Preserve its Title (section 1) will typically require changing the actual title.

9. TERMINATION#

You may not copy, modify, sublicense, or distribute the Document except as expressly provided for under this License. Any other attempt to copy, modify, sublicense or distribute the Document is void, and will automatically terminate your rights under this License. However, parties who have received copies, or rights, from you under this License will not have their licenses terminated so long as such parties remain in full compliance.

10. FUTURE REVISIONS OF THIS LICENSE#

The Free Software Foundation may publish new, revised versions of the GNU Free Documentation License from time to time. Such new versions will be similar in spirit to the present version, but may differ in detail to address new problems or concerns. See http://www.gnu.org/copyleft/.

Each version of the License is given a distinguishing version number. If the Document specifies that a particular numbered version of this License "or any later version" applies to it, you have the option of following the terms and conditions either of that specified version or of any later version that has been published (not as a draft) by the Free Software Foundation. If the Document does not specify a version number of this License, you may choose any version ever published (not as a draft) by the Free Software Foundation.

ADDENDUM: How to use this License for your documents#

Copyright (c) YEAR YOUR NAME.
   Permission is granted to copy, distribute and/or modify this document
   under the terms of the GNU Free Documentation License, Version 1.2
   or any later version published by the Free Software Foundation;
   with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts.
   A copy of the license is included in the section entitled “GNU
   Free Documentation License”.

If you have Invariant Sections, Front-Cover Texts and Back-Cover Texts, replace the “ with…Texts.” line with this:

with the Invariant Sections being LIST THEIR TITLES, with the
   Front-Cover Texts being LIST, and with the Back-Cover Texts being LIST.

If you have Invariant Sections without Cover Texts, or some other combination of the three, merge those two alternatives to suit the situation.

If your document contains nontrivial examples of program code, we recommend releasing these examples in parallel under your choice of free software license, such as the GNU General Public License, to permit their use in free software.