One copy at a time

Patterns 5 · 3:01

A job that polls a system has to run as one copy, even when two agents run the integration. singleton: true in the integration's file lets one copy lead, and a standby takes over when the leader's agent stops.

Download the mp4Recorded on 2026.2

What it covers

Two copies of hello on the agents dev and dev2, so every message is logged twice
The line singleton: true, and the four kinds that run one copy by default
A leader and its standbys, elected through Weik.io's own lock
Version 0.1.5 from weikio run, with the roles leader and standby in weikio get fleet
A takeover when the leading copy's agent stops, after which weikio logs still shows one line per tick
The admin UI marking the stopped agent Offline and then Standby once it's back, with the newest leader change listed first

Commands in this video

Terminal

$ weikio run ./hello --no-logs
$ weikio get fleet --env devtest
$ weikio logs sandbox/hello --since 15s --query 'hello again'

Transcript

0:01Polling work must happen once, not twice,
0:04but two agents keep it running when one stops.
0:13hello runs a copy on each agent, dev and dev2.
0:17Its route logs hello again every three seconds, once from each copy.
0:24Weik.io can hold hello to one running copy,
0:27with a standby stepping in when its agent stops.
0:35A single line in hello's file makes it run one copy at a time,
0:39instead of a copy on every agent that takes it.
0:42Four kinds default to this: mft, schedule, change tracking, event source.
0:52The copies elect a leader through the platform's own lock,
0:55kept in your Weik.io installation.
1:00The same lock reaches every copy.
1:03Every agent starts a copy, one leads and logs,
1:06the standby holds its routes and stands by.
1:12If the agent behind the leader stops,
1:14a standby leads again within about two seconds.
1:21hello's file has no singleton line yet, so add one.
1:26weikio run uploads, builds and deploys hello,
1:30so both copies restart on the new version.
1:37weikio get fleet for devtest lists one leader and one standby,
1:42both on the new version.
1:46The leader's agent stops.
1:48hello's log still gets one line a tick, now from one copy.
1:53The standby steps up and leads.
1:58The fleet list now marks the stopped agent offline with its role blank.
2:03The other copy still leads.
2:09The stopped agent reads Offline, with No standby above the table.
2:17The agent is back.
2:19Its copy stands by, and the leader keeps the lead.
2:27The returned copy reads Standby.
2:30The Leader changes fold lists changes newest first.
2:37A single line keeps hello to one running copy, so each message is logged once.
2:43The copies elect their leader through the platform's own lock inside your installation,
2:48the rest stand by.
2:49When a leader's agent stops, a standby takes the lead.