using consul to configure task in nomad

[dma...@istreamplanet.com]

This seems like a pretty basic use case, so I'm surprised I haven't found documentation for it yet.  Sorry if this is something covered elsewhere.

I have a job with two tasks where one needs the other to work.  One is kafka-manager which needs zookeeper to work.  I've got zookeeper registered with consul.  How do I tell nomad to use the info from consul during the launch of kafka-manager?  EG how do I zookeeper service info from consul into the nomad env section?

Thanks!

-Dylan 

[kunal kaul]

You can use consultemplate notation in the template stanza of the nomad job file to get the info into a file which would be available to your application to read.

[Sébastien Portebois]

Hi Dylan

The template stanza, relying on Consul Template, seems to be your exact use case. (Look for {{ key ..}} sample in the docs)

Here's a job using the sample http-echo server and Consul to return the content of the configs/test-echo/test key stored in Consul:

job "echo-consul" {

  type = "service"

  datacenters = ["dc1"]

  group "echo" {

    count = 1

    task "http-server" {

      driver = "docker"

      config {

        image = "hashicorp/http-echo:latest"

        args = [

          "-text", "'hello '${ECHO_VALUE}'",

          "-listen", ":${NOMAD_PORT_http}",

        ]

        port_map {

          http = "${NOMAD_PORT_http}"

        }

      }

      resources {

        network {

           port "http" {

            static = 80

          }

        }

      }

      template {

        env         = true

        data = <<EOH

ECHO_VALUE="{{key "configs/test-echo/test"}}"

EOH

        destination = "secrets/config.env"

        change_mode = "restart"

      }

      service {

        port = "http"

[dma...@istreamplanet.com]

Awesome!  Thanks!  Does nomad know to restart the dependant service if the values in consul change?  Does it know to hold off starting if the consul value isn't there?  Thanks again!

[Sébastien Portebois]

Yes, template watches for changes in the Consul KV store.
In fact that's why I left the explicit  change_mode = "restart" (which is the default, so this isn't required, but it makes the restart trigger obvious). You can also have a look at the splay argument (to control how fast it reacts to changes). With this example, it's quite easy to test it with a simple curl in a loop to query your echo server, and in the meantime you update the value in Consul, and you can observe how the allocations change, or what is the returned value by the small echo service (i.e. when the allocation of the update is running)

Re the missing value: the job will be "blocked" in pending mode because of the missing value 

IN Nomad UI, for this new allocation you'll see in the recent event a 

Template

=> Missing: kv.block(missing)

event entry

Which you'll also see with the the nomad alloc status: (bold and underline added for emphasis)

$ nomad alloc status e68373f4

ID                  = e68373f4

Eval ID             = e4d63ffe

Name                = echo-consul.echo[0]

Node ID             = bbd6bc91

Job ID              = echo-consul

Job Version         = 1

Client Status       = pending

Client Description  = <none>

Desired Status      = run

Desired Description = <none>

Created             = 2m36s ago

Modified            = 2m24s ago

Task "http-server" is "pending"

Task Resources

CPU      Memory   Disk     IOPS  Addresses

100 MHz  300 MiB  300 MiB  0     http: 10.255.103.106:80

Task Events:

Started At     = N/A

Finished At    = N/A

Total Restarts = 0

Last Restart   = N/A

Recent Events:

Time                       Type        Description

2018-09-12T13:21:04-04:00  Template    Missing: kv.block(missing)

2018-09-12T13:21:01-04:00  Task Setup  Building Task Directory

2018-09-12T13:21:01-04:00  Received    Task received by client

[dma...@istreamplanet.com]

Perfect!  Thanks so much!

On Tuesday, September 11, 2018 at 12:09:06 PM UTC-7, dma...@istreamplanet.com wrote: