The Couchbase Node is responsible for starting up an instance of Couchbase server. In addition it is responsible for registering it's self as available for clustering
- Each cluster node is disposable when replication at a bucket level is enabled
- Each cluster node runs a disposable docker container activated by a global Fleet Systemd Unit on CoreOS
- Every time the systemd unit recylces
- Removes an existing labels associated within it from a backend store (e.g. etcd)
- Starts the couchbase docker container.
- Writes a label registering it's self with the backend store for initialization
The scheduler is responsible for keeping the cluster balanced. Rebalancing the cluster as new cluster node are detected. Rebalancing when cluster nodes are no longer detected.
- The scheduler runs a loop monitoring\capturing the current state of the cluster
- The scheduler schedules actions upon detection of differences between current state and the previous state in the hope of realizing a cluster desired state
The enforcer is responsible for transitioning cluster nodes to become initialized and rebalancing the cluster
- The enforcer connects to new nodes issuing node initialization requests
- The enforcer connects to active nodes and issues rebalance requests
In line with the Unix philosophy a number of existing components will be attempted to be reused to achieve this goal.
- Couchbase Node (Dockerfile)
- Scheduler (Confd + Util)
- Enforcer (Couchbase-init)