Remarks about the “confab” wrapper for consul

Benjamin Gandon

Hi cf devs,

I’m running a CF deployment with redundancy, and I just experienced my consul servers not being able to elect any leader.
That’s a VERY frustrating situation that keeps the whole CF deployment down, until you get a deeper understanding of consul, and figure out they just need a silly manual 'join' so that they get back together.

But that was definitely not easy to nail down because at first look, I could just see monit restarting the “agent_ctl” every 60 seconds because confab was not writing the damn PID file.

More specifically, the 3 consul servers (i.e. consul_z1/0, consul_z1/1 and consul_z2/0) had properly left oneanother uppon a graceful shutdown. This state was persisted in /var/vcap/store/raft/peers.json being “null” on each one of them, so they would not get back together on restart. A manual 'join' was necessary. But it took me hours to get there because I’m no expert with consul.

And until the 'join' is made, VerifySynced() was negative in confab, and monit was constantly starting and stopping it every 60 seconds. But once you step back, you realize confab was actually waiting for the new leader to be elected before it writes the PID file. Which is questionable.

So, I’m asking 3 questions here:

1. Does writing the PID file in confab that late really makes sense?
2. Could someone please write some minimal documentation about confab, at least to tell what it is supposed to do?
3. Wouldn’t it be wiser that whenever any of the consul servers is not here, then the cluster gets unhealthy?

With this 3rd question, I mean that even on a graceful TERM or INT, no consul server should not perform any graceful 'leave'. With this different approach, then they would properly be back up even when performing a complete graceful restart of the cluster.

This can be done with those extra configs from the “confab” wrapper:

"skip_leave_on_interrupt": true,
"leave_on_terminate": false

What do you guys think of it?


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