consul-template: multiple dependent templates

[Nicholas Capo]

I will soon have three nginx configs that have templating for the same services [0]. (See consul-template config below)

I am concerned that these templates will run in serial, and for a short amount of time be inconsistent. In other words, nginx would be reloaded three times, each time with a slightly updated overall config.

Is there a way to avoid this? Are the commands defered until all templates are generated? Can I have multiple source and destination stanzas with a single command?

Nicholas

[0] I know, our setup is kinda complex, but not yet complicated: https://www.python.org/dev/peps/pep-0020/

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template {

  source = "/etc/consul-template/nginx/nginx.tmpl"

  destination = "/etc/nginx/sites-enabled/example.com"

  command = "sudo /etc/init.d/nginx reload"

}

template {

  source = "/etc/consul-template/nginx/localhost.tmpl"

  destination = "/etc/nginx/sites-enabled/localhost"

  command = "sudo /etc/init.d/nginx reload"

}

template {

  source = "/etc/consul-template/nginx/upstreams.tmpl"

  destination = "/etc/nginx/sites-enabled/upstreams"

  command = "sudo /etc/init.d/nginx reload"

}

[Seth Vargo]

Hi Nicholas,

I believe you want to use the quiescence timers build into Consul Template. Essentially you can tell Consul Template to `-wait` for a minimum and maximum amount of time for data to become "stable", does that make sense? For example:

    consul-template -wait 10s

Tells CT to wait until no new data is returned from Consul for 10 seconds. Similarly:

    consul-template -wait 10s:100s

Tells CT to wait until no new data is returned from Consul for 10 seconds, but to force continuation after 100 seconds.

Best,

Seth

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[Nicholas Capo]

Good, then when the data is stable will it do the following?

1. generate template 1

  a. reload nginx

2. generate template 2

  a. reload nginx

3. generate template 3

  a. reload nginx

Or  will it:

1. generate template 1

2. generate template 2

3. generate template 3

4. reload nginx

Its the intermediate reloads that I'm worried about.

Nicholas

[David Neudorfer]

I'm looking for an answer to this as well.

[Adam Greene]

hey folks,

you may  have already figured this out, but if not, check out the new `exec` functionality in consul-template master (https://github.com/hashicorp/consul-template#exec-mode) .  I ran into the same issue and the exec functionality solved it for me.

[Roberto Frutos]

Will it be possible to use exec mode in backgroud in the future?
Why only foreground?

It'd be a really great approach if we can run command with exec mode in backgroud/foreground.

[Seth Vargo]

If it runs in the background, it's no longer "exec", it would be a process supervisor and then Consul Template would be responsible for monitoring that process. How would it report back to the parent, etc? This is why you typically run CT under a processor monitor like init.d or upstart or systemd.

Best,

Seth