Using input variables: map type variables

Avatar
Ron Savoia
  • Updated

 

Introduction

Variables are a great way to minimize the complexity and improve the readability of your jobs; generally speaking, you would want to specify a default value to be used in case none are provided when the job is run. Nomad also allows for complex type variables, such as maps, which also accept input variables when the job is run.

A variable declared in your jobspec can be as simple as the example below

variable "image1" {
  type = string
  default = "1"
}

Using a value other than the default when running your job is achieved by adding the -var option when running your job.

nomad job run -var="image1=3" ./myjob.hcl

Note:  The -var option can be added multiple times, for each variable you've declared.

 

Variable maps are a bit different, in that they contain more than one entry for the variable.

variable "test" {
  type = map(string)
    default = {
      ex1 = "4"
      ex2 = "5"
      ex3 = null
      ex4 = null
     }
}

 

Expected Outcome

By the end of this article, you will be able to declare variable maps in your jobs and will be able to override the defaults when running your job.

Prerequisites

First, you'll want to create a jobspec which uses a variable of type map, below is an example that can be used/modified for your use case.

 

# myjob2.hcl
variable "test" {
    type = map(string)
    default = {
       ex1 = "4"
       ex2 = "5"
       ex3 = null
       ex4 = null
    }
}

job "myjob" {
datacenters = ["dc1"]
type = "service"

  group "grp1" {
      count = 1
      task "task1" {
        driver = "docker"

        config {
          image = "redis:${var.test["ex1"]}"
        }
      }
  }
  group "grp2" {
    count = 1
    task "task2" {
      driver = "docker"

      config {
        image = "redis:${var.test["ex2"]}"
      }
     }
  }
}

Procedure

  • Run your job and include the -var option so that ex1 and ex2 will use 7 and 6 respectively
    $ nomad job run -var='test={"ex1":"7","ex2":"6","ex3":null,"ex4":null}' ./myjob2.hcl

  • Next, view the running allocations to check the Redis version used for the deployment.

    $ nomad status myjob
    ID = myjob
    Name = myjob
    Submit Date = 2023-10-24T16:54:27Z
    Type = service
    Priority = 50
    Datacenters = dc1
    Namespace = default
    Node Pool = default
    Status = running
    Periodic = false
    Parameterized = false

    Summary
    Task Group Queued Starting Running Failed Complete Lost Unknown
    grp1 0 0 1 0 0 0 0
    grp2 0 0 1 0 0 0 0

    Latest Deployment
    ID = 114d7c40
    Status = successful
    Description = Deployment completed successfully

    Deployed
    Task Group Desired Placed Healthy Unhealthy Progress Deadline
    grp1 1 1 1 0 2023-10-24T17:04:43Z
    grp2 1 1 1 0 2023-10-24T17:04:49Z

    Allocations
    ID Node ID Task Group Version Desired Status Created Modified
    4cb2b3ea 21915867 grp2 0 run running 4m11s ago 3m49s ago
    bd7f533c 21915867 grp1 0 run running 4m11s ago 3m54s ago

  • Finally, view the allocation logs for each task (The redis versions should be 6 & 7 respectively)

    $ nomad alloc logs bd7f533c task1
    1:C 24 Oct 2023 16:54:33.336 # WARNING Memory overcommit must be enabled! Without it, a background save or replication may fail under low memory condition. Being disabled, it can also cause failures without low memory condition, see https://github.com/jemalloc/jemalloc/issues/1328. To fix this issue add 'vm.overcommit_memory = 1' to /etc/sysctl.conf and then reboot or run the command 'sysctl vm.overcommit_memory=1' for this to take effect.
    1:C 24 Oct 2023 16:54:33.337 * oO0OoO0OoO0Oo Redis is starting oO0OoO0OoO0Oo
    1:C 24 Oct 2023 16:54:33.337 * Redis version=7.2.2, bits=64, commit=00000000, modified=0, pid=1, just started
    1:C 24 Oct 2023 16:54:33.337 # Warning: no config file specified, using the default config. In order to specify a config file use redis-server /path/to/redis.conf
    1:M 24 Oct 2023 16:54:33.337 * monotonic clock: POSIX clock_gettime
    1:M 24 Oct 2023 16:54:33.338 * Running mode=standalone, port=6379.
    1:M 24 Oct 2023 16:54:33.338 * Server initialized
    1:M 24 Oct 2023 16:54:33.338 * Ready to accept connections tcp

    $ nomad alloc logs 4cb2b3ea task2
    1:C 24 Oct 2023 16:54:39.070 # oO0OoO0OoO0Oo Redis is starting oO0OoO0OoO0Oo
    1:C 24 Oct 2023 16:54:39.070 # Redis version=6.2.14, bits=64, commit=00000000, modified=0, pid=1, just started
    1:C 24 Oct 2023 16:54:39.070 # Warning: no config file specified, using the default config. In order to specify a config file use redis-server /path/to/redis.conf
    1:M 24 Oct 2023 16:54:39.070 * monotonic clock: POSIX clock_gettime
    1:M 24 Oct 2023 16:54:39.071 * Running mode=standalone, port=6379.
    1:M 24 Oct 2023 16:54:39.071 # Server initialized
    1:M 24 Oct 2023 16:54:39.071 # WARNING Memory overcommit must be enabled! Without it, a background save or replication may fail under low memory condition. Being disabled, it can can also cause failures without low memory condition, see https://github.com/jemalloc/jemalloc/issues/1328. To fix this issue add 'vm.overcommit_memory = 1' to /etc/sysctl.conf and then reboot or run the command 'sysctl vm.overcommit_memory=1' for this to take effect.
    1:M 24 Oct 2023 16:54:39.072 * Ready to accept connections

     

Additional Information

  • You can find additional information about HCL2 variables and their usage here.

Articles in this section

See more

Related articles