etcd #0
Description
A highly-available key value store for shared configuration and service discovery. etcd is inspired by Apache ZooKeeper and doozer, with a focus on being:
Simple: curl'able user facing API (HTTP+JSON) Secure: optional SSL client cert authentication Fast: benchmarked 1000s of writes/s per instance Reliable: properly distributed using Raft
etcd is written in Go and uses the Raft consensus algorithm to manage a highly-available replicated log.
Etcd
Etcd is a highly available distributed key value store that provides a reliable way to store data across a cluster of machines. Etcd gracefully handles master elections during network partitions and will tolerate machine failure, including the master.
Your applications can read and write data into etcd. A simple use-case is to store database connection details or feature flags in etcd as key value pairs. These values can be watched, allowing your app to reconfigure itself when they change.
Advanced uses take advantage of the consistency guarantees to implement database master elections or do distributed locking across a cluster of workers.
Etcd allows storing data in a distributed hierarchical database with observation.
Usage
We can deploy a single node easily with
juju deploy cs:trusty/etcd
Add and capacity with:
juju add-unit -n 2 etcd
Its recommended to run an odd number of machines as it has greater redundancy than even number (ie. 4, you can lose 1 before quorum is lost, where as 5, you can 2).
Advanced Usage
This charm also supports a proxy relation, when using the ETCD cluster as a
discovery service for your own applications. Reference the
upstream documentation
to learn more about this feature of ETCD
juju add-relation <service>:<relation> etcd:proxy
For each node in the cluster, you will receive a cluster-string that you can use to point your application into the cluster and join the gossip.
Health
Health of the cluster can be checked by verified via juju actions
juju action do etcd/0 health
<return response uuid>
juju action fetch <uuid>
Usage Caveats
This charm requires Leader Election, which is a feature of Juju >= 1.23.2. The charm will panic and refuse to continue if the leader_election binary is not found. Please take care when deploying this charm on older versions of Juju.
Credits
The etcd charm was originally written by Kapil Thangavelu (@kapilt).
Maintainers:
The kubernetes team maintains this charm: - Whit Morriss <whit.morriss@canonical.com> - Charles Butler <charles.butler@canonical.com> - Matt Bruzek <matthew.bruzek@canonical.com>