consul-lock: a pack demonstrating Consul leadership election

[tgross]

A pack that demonstrates a script for ensuring that a single Nomad allocation of a job is running at one time. Based on the Consul Learn Guide for application leader elections.

[tgross]

Moving this back to draft b/c I somehow broke it. Need to retest. Figured that out... I needed an extra refresh loop for the blocking case and I'd never left it blocking long enough in my bench testing to hit that case.

[MikaelHashiCorp]

This pack fails for me.

SETUP

vagrant@pack:~/nomad-autoscaler/jobs$ nomad-pack registry add default github.com/mikaelhashicorp/nomad-pack-community-registry --target=consul_lock
go-getter URL is github.com/mikaelhashicorp/nomad-pack-community-registry.git//packs/consul_lock
Registry successfully cloned at /home/vagrant/.cache/nomad/packs/nomad-pack-tmp
Processing pack entries at /home/vagrant/.cache/nomad/packs/nomad-pack-tmp
found pack entry consul_lock
Processing pack consul_lock@latest
Updating pack
Removing previous latest
Writing pack to /home/vagrant/.cache/nomad/packs/default/consul_lock@latest
Loading cloned pack from /home/vagrant/.cache/nomad/packs/default/consul_lock@latest
Calculating SHA for latest
error calculating SHA
  temp directory deleted
  Registry successfully added to cache.
   PACK NAME  |  REF   | METADATA VERSION | REGISTRY |     REGISTRY URL      
--------------+--------+------------------+----------+-----------------------
  consul_lock | latest | 0.1.0            | default  | github.com/hashicorp  

  Try running one the packs you just added liked this
  
    nomad-pack run consul_lock --registry=default --ref=latest

vagrant@pack:~/nomad-autoscaler/jobs$ nomad-pack info consul_lock
Pack Name          consul_lock
Description        A pack demonstrating the use of Consul session locks for ensuring that only a single allocation of a job is running at a time.
Application URL    https://learn.hashicorp.com/tutorials/consul/application-leader-elections
Application Author HashiCorp, Inc.

Pack "consul_lock" Variables:
        - "constraints" (list of object) - Additional constraints to apply to the jobs.
        - "resources" (object) - The resources to assign to the main task.
        - "namespace" (string) - The namespace for the job.
        - "locker_key" (string) - The path to the locker script
        - "application_image" (string) - The container image for the main task.
        - "application_args" (string) - The command and args for the main task's application.
        - "application_port_name" (string) - The name of the port the application listens on.
        - "application_port" (string) - The port the application listens on.
        - "job_name" (string) - The name of the job.
        - "datacenters" (list of string) - A list of datacenters in the region which are eligible for task placement.
        - "region" (string) - The region where the job should be placed.
        - "locker_image" (string) - The container image for the lock task (needs curl).
        - "locker_script_path" (string) - The path to the locker script

ERRORS

• Doing command nomad-pack render consul_lock fails with nil pointer:

vagrant@pack:~/nomad-autoscaler/jobs$ nomad-pack render consul_lock
! Failed To Process Pack

        Error:   failed to render consul_lock/templates/example.nomad.tpl: template: consul_lock/templates/example.nomad.tpl:1:11: executing "consul_lock/templates/example.nomad.tpl" at <.my.job_name>: nil pointer
evaluating interface {}.job_name
        Type:    *errors.errorString
        Context: 
                 - Registry Name: default
                 - Pack Name: consul_lock
                 - Pack Ref: latest

• Doing command nomad-pack plan consul_lock fails with nil pointer:

vagrant@pack:~/nomad-autoscaler/jobs$ nomad-pack plan consul_lock
! Failed To Process Pack

        Error:   failed to render consul_lock/templates/example.nomad.tpl: template: consul_lock/templates/example.nomad.tpl:1:11: executing "consul_lock/templates/example.nomad.tpl"
at <.my.job_name>: nil pointer evaluating interface {}.job_name
        Type:    *errors.errorString
        Context: 
                 - Registry Name: default
                 - Pack Name: consul_lock
                 - Pack Ref: latest
                 - Deployment Name: consul_lock@latest

• Doing command nomad-pack run consul_lock --registry=default --ref=latest fails with nil pointer:

vagrant@pack:~/nomad-autoscaler/jobs$ nomad-pack run consul_lock --registry=default --ref=latest
! Failed To Process Pack

        Error:   failed to render consul_lock/templates/example.nomad.tpl: template: consul_lock/templates/example.nomad.tpl:1:11: executing "consul_lock/templates/example.nomad.tpl" at
<.my.job_name>: nil pointer evaluating interface {}.job_name
        Type:    *errors.errorString
        Context: 
                 - Registry Name: default
                 - Pack Name: consul_lock
                 - Pack Ref: latest
                 - Deployment Name: consul_lock@latest

[MikaelHashiCorp]

Reference to the nil pointer issue: https://discuss.hashicorp.com/t/nil-pointer-evaluating-interface-region/32973
Reference to .my. issue: hashicorp/nomad-pack#248

[tgross]

@MikaelHashiCorp can you explain what you mean with those two links? I see in your error log that there's a nil pointer on the template for some reason but as far as I can tell the value is set as the default variable. Is there some insight in those links that suggests why?

[MikaelHashiCorp]

@tgross:

• When I run the consul-lock pack, I get the nul pointer issue. The link, Nil pointer evaluating interface {}.region, is to show it isn't just me and it was claimed to be a bug by @lgfa29. I cannot find the GitHub issue for that bug.
• When I run any pack with .my. used in the templates, such as redis, chaotic_ngine, and jaeger, I get the nul pointer issue. This tells me they are related somehow. I found issue: docs: add documentation around .my. root level variable namespacing #248 by @jrasell, thinking it might be related, but I don't know how to interpret that issue posting.

I referenced the two links in case they may help you in anyway.