Add check_leader command to lavinmqctl

[annieblomgren]

Summary

This adds a check_leader command to lavinmqctl that quickly displays which node is the current cluster leader.

Motivation

The existing cluster_status command shows this_node, version, and followers, but there's no dedicated way to quickly check which node is the leader. In scripting and monitoring scenarios, a lightweight single-purpose command is more convenient than parsing the full cluster status output.

Since lavinmqctl always communicates with the leader node (followers either return 503 on the internal socket or proxy HTTP requests to the leader), the name field from /api/nodes reliably identifies the leader.

Usage

$ lavinmqctl check_leader
leader: MacBook-Pro-4.local

$ lavinmqctl check_leader --format=json
{"leader":"MacBook-Pro-4.local"}

Implementation

The command calls the existing /api/nodes API endpoint, extracts the first node's name field, and outputs it. It follows the same pattern as status and cluster_status — no new API endpoints or dependencies are needed.

Files changed:

• src/lavinmqctl/cli.cr — command registration, dispatch, and implementation
• spec/lavinmqctl_spec.cr — test

Branch: add-leader-command

Use cases

• Health checks / monitoring: Quickly verify which node is leading the cluster
• Scripting: LEADER=$(lavinmqctl check_leader --format=json | jq -r .leader) for use in automation
• Debugging: Fast confirmation of leader identity during cluster troubleshooting

[annieblomgren]

just an idea from Claude, Erik, Håkan and I :)