Consul: Proposal: One-off commands through `consul lock`

[JensRantil]

Usecase: I have a shell command I'd like to execute once on a bunch of Consul agent hosts. I only want a concurrency level of X to not choke the system. This sounds like a perfect usecase for a semaphore. However, implementing semaphore for a shell script is cumbersome. consul lock supports semaphore, but it will restart my shell command over and over again.

Proposal: Add a consul lock -oneoff parameter that acquires a semaphore, executes the command and then exits. What do you think?

Workaround: I could use the restarting consul lock my-script.sh and have my script do something like:

#!/bin/sh

# Check if file XXX exists. If so, sleep 5 seconds (to not spin CPU) and then quit.
# Create the file XXX
# Run my command

[JensRantil]

A different workaround is to have the script kill the consul lock command (using something like $PPID) when it's done.

[jippi]

name wise -once would be more consistent - i like the idea though :)

[JensRantil]

;) I'm totally fine with -once.

[JensRantil]

I got started implementing a shell semaphore (with jq dependency) https://gist.github.com/JensRantil/4173e4f1ecf031f3f263e5a1c2f5f861 Gave up after a while.

[slackpad]

Hi @JensRantil have you looked at the consul lock command? If I understand your use case correctly I think it does exactly what you are looking for :-)

consul lock -n=<concurrency> /some/lock/prefix yourscript.sh

This will run up to n at any given time and will simply execute the command and then exit.

[JensRantil]

@slackpad Slackpad. Rereading the documentation I now see that the consul lock command doesn't restart a command! 👍 Closing this!