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mehdb

This is mehdb, an educational Kubernetes-native NoSQL data store. It is not meant for production usage but purely to learn and experiment with StatefulSets.

Usage

Deploy it:

$ kubectl create ns mehdb
$ kubectl -n=mehdb apply -f app.yaml

Access it from within the cluster:

$ kubectl -n=mehdb run -i -t --rm jumpod --restart=Never --image=quay.io/mhausenblas/jump:0.2 -- sh
$ echo "test data" > /tmp/test
$ curl -L -XPUT -T /tmp/test mehdb:9876/set/test
$ curl mehdb:9876/get/test
$ curl mehdb-1.mehdb:9876/get/test

Scale to 3 shards (1 leader, 2 followers):

$ kubectl -n=mehdb scale sts mehdb --replicas=4

Clean up:

$ kubectl -n=mehdb delete sts/mehdb
$ kubectl -n=mehdb delete pvc/data-mehdb-0
$ kubectl -n=mehdb delete pvc/data-mehdb-1
$ kubectl -n=mehdb delete svc/mehdb

Note: I tested it in OpenShift Online with Kubernetes in version 1.9 and the setup assumes that a storage class ebs exists.

API

Once deployed you can use mehdb to store and retrieve data. Keep the following in mind:

  • The keys are restricted, that is, they must match [a-z]+. For example, abc is a valid key, 123 or _mykey42 is not.
  • The leader shard accepts both reads and writes, a follower shard will redirect to the leader shard if you attempt a write operation.

The following public endpoints are available:

/get/$KEY … a HTTP GET at this endpoint retrieves the payload available under the key $KEY or a 404 if the key does not exist.

/set/$KEY … a HTTP PUT at this endpoint stores the payload provided under the key $KEY.

/status … by default returns a 200 and the role (leader or follower), which can be used for a liveness probe, with ?level=full it returns a 200 and the number of keys it can serve, which can be used for a readiness probe.

Local development

Run a leader shard like so:

$ MEHDB_HOST=mehdb-0 MEHDB_PORT=9999 go run main.go

Run a follower shard like so:

$ MEHDB_LOCAL=yes MEHDB_DATADIR=./follower-data go run main.go

Now you can for example write to and/or read from the leader:

$ http PUT localhost:9999/set/abc < test/somedata
$ http localhost:9999/get/abc

Also, you can read from the follower:

$ http localhost:9876/get/abc

If you try to write to the follower, you'll be redirected:

$ http PUT localhost:9876/set/abc < test/somedata
HTTP/1.1 307 Temporary Redirect
Content-Length: 0
Date: Tue, 19 Jun 2018 12:28:57 GMT
Location: http://localhost:9999/set/abc