How to run an etcd cluster among pod replicas?
I have a pod/service running an application that consumes etcd as a synchronization system and datastore. I want to run etcd within the pod, such that all of the replicas form a coherent cluster. In other words, so the application in replica #1 can write "foo" to localhost:4001/v2/keys/my_key and then replica #2 can then read localhost:4001/v2/keys/my_key and get "foo" as a result.
It's not clear how this can be done, since pod replicas are not individually addressable. I could in theory create an "etcd" service exposing the cluster ports, but any requests would round-robin to all the replicas so the individual etcd nodes would not be able to find each other.
Am I approaching this problem the correct way?
You can deploy etcd on kubernetes using an Operator (from the extensions/v1beta1 ) and the quay.io/coreos/etcd-operator image.
An example deployment with a cluster size of 3 looks like this:
apiVersion: extensions/v1beta1
kind: Deployment
metadata:
name: etcd-operator
spec:
replicas: 1
template:
metadata:
name: etcd-operator
labels:
app: etcd
component: operator
spec:
containers:
- name: etcd-operator
image: quay.io/coreos/etcd-operator:v0.3.0
env:
- name: MY_POD_NAMESPACE
valueFrom: { fieldRef: { fieldPath: metadata.namespace } }
- name: MY_POD_NAME
valueFrom: { fieldRef: { fieldPath: metadata.name } }
---
apiVersion: etcd.coreos.com/v1beta1
kind: Cluster
metadata:
name: etcd-cluster
labels:
app: etcd
component: cluster
spec:
size: 3
version: "3.1.8"
Please be aware of the beta status of this project. However according to the maintainers the operator is now stable . I have deployed the configuration above successfully but I didn't run any of this in production.
The operator code is available on github. You can find additional documentation there.
There's a pretty good example of a three node etcd cluster here: https://github.com/coreos/etcd/tree/master/hack/kubernetes-deploy
They make use of separate rc's and services for each replica as a workaround until nominal services are added.
I added your question to kubernetes/kubernetes#5017
If someone knows the answer, they will hopefully post it there.
I think it may require the "nominal services" feature (kubernetes/kubernetes#260) which is not implemented yet, but I'm not sure.
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