role-labels

This application shows a simple use-case of labels where the labels of a node will describe the role the member is fulfilling in the cluster. All nodes are able to list the nodes that fulfill a specific role.

Note: this file can be cram-executed using make test-examples. That's why some of the example outputs below are a bit unusual.

Running the example

All commands are relative to this directory:

$ cd ${TESTDIR}  # examples/role-labels

(optional, the files are already included) Generate the thrift code:

$ go generate

Build the example binary:

$ go build

Start a custer of 5 nodes using tick-cluster:

$ tick-cluster.js --interface=127.0.0.1 -n 5 role-labels &> tick-cluster.log &
$ sleep 5

Show all nodes that fulfill the roleA role using tcurl:

$ tcurl role -P hosts.json --thrift ./role.thrift RoleService::GetMembers '{"role":"roleA"}'
{"ok":true,"head":{},"body":["127.0.0.1:300?","127.0.0.1:300?","127.0.0.1:300?","127.0.0.1:300?","127.0.0.1:300?"],"headers":{"as":"thrift"},"trace":"*"} (glob)

This will give you the list of all instances as they all start with their role set to roleA. The role of an instance can be changed by running:

$ tcurl role -P hosts.json --thrift ./role.thrift RoleService::SetRole '{"role":"roleB"}'
{"ok":true,"head":{},"headers":{"as":"thrift"},"trace":"*"} (glob)
$ sleep 2 # give the cluster of 5 some time to converge on the new state of the membership

To validate that this worked we can now lookup both the members for roleA and roleB and see that the membership lists contain respectively 4 and 1 member:

$ tcurl role -P hosts.json --thrift ./role.thrift RoleService::GetMembers '{"role":"roleA"}'
{"ok":true,"head":{},"body":["127.0.0.1:300?","127.0.0.1:300?","127.0.0.1:300?","127.0.0.1:300?"],"headers":{"as":"thrift"},"trace":"*"} (glob)

$ tcurl role -P hosts.json --thrift ./role.thrift RoleService::GetMembers '{"role":"roleB"}'
{"ok":true,"head":{},"body":["127.0.0.1:300?"],"headers":{"as":"thrift"},"trace":"*"} (glob)

In the end you should kill tick cluster via:

$ kill %1