Add support for SignalTask.

[shishir-a412ed]

Signed-off-by: Shishir Mahajan smahajan@roblox.com

[shishir-a412ed]

This patch can be tested using the following example job.

job "example" {
  datacenters = ["dc1"]

  group "cache" {
    task "redis" {
      driver = "podman"

      config {
        image = "docker://shm32/signal_handler:1.0"

        port_map {
          db = 6379
        }
      }

      resources {
        cpu    = 500
        memory = 256

        network {
          mbits = 10
          port  "db"  {}
        }
      }
    }
  }
}

$ nomad job run example.nomad

<Second terminal>
$ nomad alloc signal -s SIGHUP 61036c06

<First terminal>
$ nomad alloc logs -f 61036c06
2020-08-18T23:12:30.081746628+00:00 stdout F Hello signal_handler. My PID is 1
2020-08-18T23:14:05.132489761+00:00 stdout F Received SIGHUP

<Second terminal>
$ nomad alloc signal -s SIGUSR1 61036c06

<First Terminal>
$ nomad alloc logs -f 61036c06
2020-08-18T23:12:30.081746628+00:00 stdout F Hello signal_handler. My PID is 1
2020-08-18T23:14:05.132489761+00:00 stdout F Received SIGHUP
2020-08-18T23:15:25.163521867+00:00 stdout F Received SIGUSR1

[towe75]

Thank you for this contribution. I want to discuss about the SIGINT fallback, otherwise it looks good to me.

[shishir-a412ed]

@towe75

[vagrant@fedora30 example]$ nomad alloc signal -s SIGHUP 08bef401
<On second terminal>
[vagrant@fedora30 example]$ nomad alloc logs -f -job example
2020-08-24T20:09:41.400344873+00:00 stdout F Hello signal_handler. My PID is 1
2020-08-24T20:10:46.421778893+00:00 stdout F Received SIGHUP


[vagrant@fedora30 example]$ nomad alloc signal -s HUP 08bef401
Error signalling allocation: Unexpected response code: 500 (1 error occurred:
	* Failed to signal task: redis, err: rpc error: code = Unknown desc = Error in looking up signal: HUP

)

[shishir-a412ed]

@towe75 I am contemplating on the error message. Which one do you think would be better?

1. Error in looking up signal: HUP

OR

2. Invalid signal: HUP

[towe75]

@shishir-a412ed I would go for the second one. Less words are usually better ;-)
But i don't mind if you keep first one.

[shishir-a412ed]

@towe75 Sounds good! I was leaning towards (2) as well.
Already made the same change in our containerd task driver: Roblox/nomad-driver-containerd#34

Let me update the PR.

[shishir-a412ed]

@towe75 Updated the error message. PTAL.

[towe75]

LGTM 🚀