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Sphinx and OpenStack documentation standards require the use of RST formatted documentation. In order to get out docs integrated into docs.openstack.org, the following steps must be taken: 1. we need to first convert the documentation to RST 2. sphinx support must be added to the repository 3. project-config must be updated with a publish-docs job The ability to pubish to docs.openstack.org is a privilege only available to Big Tent projects. As a result, we should be taking advantage of this to help spread the word on our implementation. Note the documentation was converted with a tool called pandoc the syntax of which was: pandoc -f markdown -t rst file.md > z mv z file.rst In order for git to preserve history the files have to be git mv'ed in one commit followed by the pandoc operation in a separate commit. Change-Id: Iba2a70b989e8305da03e8204a9b130d457b00cf0 |
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| README.rst | ||
| redis-controller.yaml | ||
| redis-master.yaml | ||
| redis-proxy.yaml | ||
| redis-sentinel-controller.yaml | ||
| redis-sentinel-service.yaml | ||
## Reliable, Scalable Redis on Kubernetes
The following document describes the deployment of a reliable, multi-node Redis on Kubernetes. It deploys a master with replicated slaves, as well as replicated redis sentinels which are use for health checking and failover.
### Prerequisites This example assumes that you have a Kubernetes
cluster installed and running, and that you have installed the
`kubectl` command line tool somewhere in your path. Please
see the [getting started](https://github.com/GoogleCloudPlatform/kubernetes/tree/master/docs/getting-started-guides)
for installation instructions for your platform.
### A note for the impatient This is a somewhat long tutorial. If you want to jump straight to the "do it now" commands, please see the [tl; dr](#tl-dr) at the end.
### Turning up an initial master/sentinel pod. is a [_Pod](https://github.com/GoogleCloudPlatform/kubernetes/blob/master/docs/pods.md). A Pod is one or more containers that _must be scheduled onto the same host. All containers in a pod share a network namespace, and may optionally share mounted volumes.
We will used the shared network namespace to bootstrap our Redis
cluster. In particular, the very first sentinel needs to know how to
find the master (subsequent sentinels just ask the first sentinel).
Because all containers in a Pod share a network namespace, the sentinel
can simply look at `$(hostname -i):6379`.
Here is the config for the initial master and sentinel pod: [redis-master.yaml](redis-master.yaml)
Create this master as follows:
`sh kubectl create -f examples/redis/v1beta3/redis-master.yaml`
### Turning up a sentinel service In Kubernetes a _Service describes a set of Pods that perform the same task. For example, the set of nodes in a Cassandra cluster, or even the single node we created above. An important use for a Service is to create a load balancer which distributes traffic across members of the set. But a _Service can also be used as a standing query which makes a dynamically changing set of Pods (or the single Pod we've already created) available via the Kubernetes API.
In Redis, we will use a Kubernetes Service to provide a discoverable endpoints for the Redis sentinels in the cluster. From the sentinels Redis clients can find the master, and then the slaves and other relevant info for the cluster. This enables new members to join the cluster when failures occur.
Here is the definition of the sentinel service:[redis-sentinel-service.yaml](redis-sentinel-service.yaml)
Create this service:
`sh kubectl create -f examples/redis/v1beta3/redis-sentinel-service.yaml`
### Turning up replicated redis servers So far, what we have done is
pretty manual, and not very fault-tolerant. If the
`redis-master` pod that we previously created is destroyed
for some reason (e.g. a machine dying) our Redis service goes away with
it.
In Kubernetes a _Replication Controller is responsible for replicating sets of identical pods. Like a _Service it has a selector query which identifies the members of it's set. Unlike a _Service it also has a desired number of replicas, and it will create or delete _Pods to ensure that the number of _Pods matches up with it's desired state.
Replication Controllers will "adopt" existing pods that match their selector query, so let's create a Replication Controller with a single replica to adopt our existing Redis server. [redis-controller.yaml](redis-controller.yaml)
The bulk of this controller config is actually identical to the redis-master pod definition above. It forms the template or "cookie cutter" that defines what it means to be a member of this set.
Create this controller:
`sh kubectl create -f examples/redis/v1beta3/redis-controller.yaml`
We'll do the same thing for the sentinel. Here is the controller config:[redis-sentinel-controller.yaml](redis-sentinel-controller.yaml)
We create it as follows:
`sh kubectl create -f examples/redis/v1beta3/redis-sentinel-controller.yaml`
### Resize our replicated pods Initially creating those pods didn't actually do anything, since we only asked for one sentinel and one redis server, and they already existed, nothing changed. Now we will add more replicas:
`sh kubectl resize rc redis --replicas=3`
`sh kubectl resize rc redis-sentinel --replicas=3`
This will create two additional replicas of the redis server and two additional replicas of the redis sentinel.
Unlike our original redis-master pod, these pods exist independently,
and they use the `redis-sentinel-service` that we defined
above to discover and join the cluster.
### Delete our manual pod The final step in the cluster turn up is to delete the original redis-master pod that we created manually. While it was useful for bootstrapping discovery in the cluster, we really don't want the lifespan of our sentinel to be tied to the lifespan of one of our redis servers, and now that we have a successful, replicated redis sentinel service up and running, the binding is unnecessary.
Delete the master as follows:
`sh kubectl delete pods redis-master`
Now let's take a close look at what happens after this pod is deleted. There are three things that happen:
- The redis replication controller notices that its desired state is 3 replicas, but there are currently only 2 replicas, and so it creates a new redis server to bring the replica count back up to 3
- The redis-sentinel replication controller likewise notices the missing sentinel, and also creates a new sentinel.
- The redis sentinels themselves, realize that the master has disappeared from the cluster, and begin the election procedure for selecting a new master. They perform this election and selection, and chose one of the existing redis server replicas to be the new master.
### Conclusion At this point we now have a reliable, scalable Redis installation. By resizing the replication controller for redis servers, we can increase or decrease the number of read-slaves in our cluster. Likewise, if failures occur, the redis-sentinels will perform master election and select a new master.
### tl; dr For those of you who are impatient, here is the summary of commands we ran in this tutorial
`sh # Create a bootstrap master kubectl create -f examples/redis/v1beta3/redis-master.yaml # Create a service to track the sentinels kubectl create -f examples/redis/v1beta3/redis-sentinel-service.yaml # Create a replication controller for redis servers kubectl create -f examples/redis/v1beta3/redis-controller.yaml # Create a replication controller for redis sentinels kubectl create -f examples/redis/v1beta3/redis-sentinel-controller.yaml # Resize both replication controllers kubectl resize rc redis --replicas=3 kubectl resize rc redis-sentinel --replicas=3 # Delete the original master pod kubectl delete pods redis-master`