Container dependency in job file

[Denriful]

I would like to run some service in nomad cluster that requires database connection. For simple example - Wordpress.

In docker-compose we can link two docker instances (frontend + db) via "depends_on" directive.

But how this can be accomplished in nomad job file?

Just a sample docker-compose that i need to convert to nomad job:

version: ‘2’
	services:
	db:
	image: mysql:5.7
	volumes:
	– db_data:/var/lib/mysql
	restart: always
	environment:
	MYSQL_ROOT_PASSWORD: wordpress
	MYSQL_DATABASE: wordpress
	MYSQL_USER: wordpress
	MYSQL_PASSWORD: wordpress
	wordpress:
	depends_on:
	– db
	image: wordpress:latest
	ports:
	– “8000:80”
	restart: always
	environment:
	WORDPRESS_DB_HOST: db:3306
	WORDPRESS_DB_PASSWORD: wordpress
	volumes:
	db_data:

[msch...@hashicorp.com]

In Nomad you would probably use Consul to discover the address of the database and Vault to retrieve the database credentials. A Wordpress job file might look something like:

job "wordpress" {

  datacenters = ["dc1"]

  group "wordpress" {

    # Scale count to handle your expected traffic

    count = 2

    task "wordpress" {

      driver = "docker"

      config {

        image = "wordpress:latest"

        port_map {

          http = 80

        }

      }

      resources {

        cpu    = 500 # 500 MHz

        memory = 256 # 256MB

        network {

          mbits = 10

          port "http" {

            static = "8000"

          }

        }

      }

      service {

        name = "wordpress"

        port = "http"

        check {

          name     = "alive"

          type     = "http"

          interval = "10s"

          timeout  = "2s"

        }

      }

      # env = true requires Nomad  0.6

      template {

        data          = <<EOF

WORDPRESS_DB_HOST={{ key "service/mysql" }}

{{ with secret "database/creds/mysql" }}

WORDPRESS_DB_USER={{ .Data.username }}

WORDPRESS_DB_PASSWORD={{ .Data.password }}

EOF

        change_mode   = "restart"

        env           = true

      }

      vault {

        policies      = ["database"]

        change_mode   = "signal"

        change_signal = "SIGHUP"

      }

    }

  }

}

Note that to configure Wordpress via environment variables requires some recent additions to Nomad, so you'll either need to build from master or wait for the upcoming 0.6 release. You could use the env stanza to hardcode the username and password, but discourage that because it's hard to keep that secure.

If you can alter the Docker image to read from a templated configuration file, you can write that from Nomad today using the template stanza: https://www.nomadproject.io/docs/job-specification/template.html

It's more involved to setup Wordpress+MySQL in Nomad, but you have much greater flexibility and a lot more features available.

Hope that helps!

[Abhishek Das]

I have similar kind of situation where I have Rabbitmq server running on docker and an java app requires IP of rabbitmq in its configuration. I am struggling to figure out that how do I pass on Rabbitmq IP to this config file. From the mentioned example I understand we can use template, however how are we storing the key service/mysql in Consul? Is it auto registered from Mysql job or do we need to manually update it? 

Regards,

Abhishek

[Chelsea Komlo]

Hi Abishek,

You can use a script to submit the Nomad job. This script could first query the Consul API and inject this value as an environment variable to the Nomad job.

See https://www.nomadproject.io/docs/runtime/interpolation.html for more information about interpolated values in Nomad.

Let us know how else we can help,

Chelsea

--
This mailing list is governed under the HashiCorp Community Guidelines - https://www.hashicorp.com/community-guidelines.html. Behavior in violation of those guidelines may result in your removal from this mailing list.
 
GitHub Issues: https://github.com/hashicorp/nomad/issues
IRC: #nomad-tool on Freenode
---
You received this message because you are subscribed to the Google Groups "Nomad" group.
To unsubscribe from this group and stop receiving emails from it, send an email to nomad-tool+unsubscribe@googlegroups.com.
To view this discussion on the web visit https://groups.google.com/d/msgid/nomad-tool/29c65574-791f-4edf-b271-07b4a63de7a6%40googlegroups.com.
For more options, visit https://groups.google.com/d/optout.