open-nomad/website/source/docs/job-specification/service.html.md

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docs	service Stanza - Job Specification	docs-job-specification-service	The "service" stanza instructs Nomad to register the task as a service using the service discovery integration.

service Stanza

Placement	job -> group -> task -> **service**

The service stanza instructs Nomad to register the task as a service using the service discovery integration. This section of the documentation will discuss the configuration, but please also read the Nomad service discovery documentation for more detailed information about the integration.

job "docs" {
  group "example" {
    task "server" {
      service {
        tags = ["leader", "mysql"]

        port = "db"

        check {
          type     = "tcp"
          port     = "db"
          interval = "10s"
          timeout  = "2s"
        }

        check {
          type     = "script"
          name     = "check_table"
          command  = "/usr/local/bin/check_mysql_table_status"
          args     = ["--verbose"]
          interval = "60s"
          timeout  = "5s"

          check_restart {
            limit = 3
            grace = "90s"
            ignore_warnings = false
          }
        }
      }
    }
  }
}

This section of the documentation only covers the job file options for configuring service discovery. For more information on the setup and configuration to integrate Nomad with service discovery, please see the Nomad service discovery documentation. There are steps you must take to configure Nomad. Simply adding this configuration to your job file does not automatically enable service discovery.

service Parameters

• check (Check: nil) - Specifies a health check associated with the service. This can be specified multiple times to define multiple checks for the service. At this time, Nomad supports the script¹, http and tcp checks.

• name (string: "<job>-<group>-<task>") - Specifies the name this service will be advertised as in Consul. If not supplied, this will default to the name of the job, group, and task concatenated together with a dash, like "docs-example-server". Each service must have a unique name within the cluster. Names must adhere to RFC-1123 §2.1 and are limited to alphanumeric and hyphen characters (i.e. [a-z0-9\-]), and be less than 64 characters in length.

  In addition to the standard Nomad interpolation, the following keys are also available:

  • ${JOB} - the name of the job
  • ${GROUP} - the name of the group
  • ${TASK} - the name of the task
  • ${BASE} - shorthand for ${JOB}-${GROUP}-${TASK}

  Validation of the name occurs in two parts. When the job is registered, an initial validation pass checks that the service name adheres to RFC-1123 §2.1 and the length limit, excluding any variables requiring interpolation. Once the client receives the service and all interpretable values are available, the service name will be interpolated and revalidated. This can cause certain service names to pass validation at submit time but fail at runtime.

• port (string: <optional>) - Specifies the label of the port on which this service is running. Note this is the label of the port and not the port number unless address_mode = driver. The port label must match one defined in the network stanza unless you're also using address_mode="driver". Numeric ports may be used when in driver addressing mode.

• tags (array<string>: []) - Specifies the list of tags to associate with this service. If this is not supplied, no tags will be assigned to the service when it is registered.

• address_mode (string: "auto") - Specifies what address (host or driver-specific) this service should advertise. This setting is supported in Docker since Nomad 0.6 and rkt since Nomad 0.7. See below for examples. Valid options are:

  • auto - Allows the driver to determine whether the host or driver address should be used. Defaults to host and only implemented by Docker. If you use a Docker network plugin such as weave, Docker will automatically use its address.

  • driver - Use the IP specified by the driver, and the port specified in a port map. A numeric port may be specified since port maps aren't required by all network plugins. Useful for advertising SDN and overlay network addresses. Task will fail if driver network cannot be determined. Only implemented for Docker and rkt.

  • host - Use the host IP and port.

check Parameters

Note that health checks run inside the task. If your task is a Docker container, the script will run inside the Docker container. If your task is running in a chroot, it will run in the chroot. Please keep this in mind when authoring check scripts.

• address_mode (string: "host") - Same as address_mode on service. Unlike services, checks do not have an auto address mode as there's no way for Nomad to know which is the best address to use for checks. Consul needs access to the address for any HTTP or TCP checks. Added in Nomad 0.7.1. See below for details. Unlike port, this setting is not inherited from the service.

• args (array<string>: []) - Specifies additional arguments to the command. This only applies to script-based health checks.

• check_restart - See check_restart stanza.

• command (string: <varies>) - Specifies the command to run for performing the health check. The script must exit: 0 for passing, 1 for warning, or any other value for a failing health check. This is required for script-based health checks.

  ~> Caveat: The command must be the path to the command on disk, and no shell exists by default. That means operators like || or && are not available. Additionally, all arguments must be supplied via the args parameter. To achieve the behavior of shell operators, specify the command as a shell, like /bin/bash and then use args to run the check.

• initial_status (string: <enum>) - Specifies the originating status of the service. Valid options are the empty string, passing, warning, and critical.

• interval (string: <required>) - Specifies the frequency of the health checks that Consul will perform. This is specified using a label suffix like "30s" or "1h". This must be greater than or equal to "1s"

• method (string: "GET") - Specifies the HTTP method to use for HTTP checks.

• name (string: "service: <name> check") - Specifies the name of the health check.

• path (string: <varies>) - Specifies the path of the HTTP endpoint which Consul will query to query the health of a service. Nomad will automatically add the IP of the service and the port, so this is just the relative URL to the health check endpoint. This is required for http-based health checks.

• port (string: <varies>) - Specifies the label of the port on which the check will be performed. Note this is the label of the port and not the port number unless address_mode = driver. The port label must match one defined in the network stanza. If a port value was declared on the service, this will inherit from that value if not supplied. If supplied, this value takes precedence over the service.port value. This is useful for services which operate on multiple ports. http and tcp checks require a port while script checks do not. Checks will use the host IP and ports by default. In Nomad 0.7.1 or later numeric ports may be used if address_mode="driver" is set on the check.

• protocol (string: "http") - Specifies the protocol for the http-based health checks. Valid options are http and https.

• timeout (string: <required>) - Specifies how long Consul will wait for a health check query to succeed. This is specified using a label suffix like "30s" or "1h". This must be greater than or equal to "1s"

• type (string: <required>) - This indicates the check types supported by Nomad. Valid options are script, http, and tcp.

• tls_skip_verify (bool: false) - Skip verifying TLS certificates for HTTPS checks. Requires Consul >= 0.7.2.

header Stanza

HTTP checks may include a header stanza to set HTTP headers. The header stanza parameters have lists of strings as values. Multiple values will cause the header to be set multiple times, once for each value.

service {
  # ...
  check {
    type     = "http"
    port     = "lb"
    path     = "/_healthz"
    interval = "5s"
    timeout  = "2s"
    header {
      Authorization = ["Basic ZWxhc3RpYzpjaGFuZ2VtZQ=="]
    }
  }
}

service Examples

The following examples only show the service stanzas. Remember that the service stanza is only valid in the placements listed above.

Basic Service

This example registers a service named "load-balancer" with no health checks.

service {
  name = "load-balancer"
  port = "lb"
}

This example must be accompanied by a network stanza which defines a static or dynamic port labeled "lb". For example:

resources {
  network {
    mbits = 10
    port "lb" {}
  }
}

Check with Bash-isms

This example shows a common mistake and correct behavior for custom checks. Suppose a health check like this:

$ test -f /tmp/file.txt

In this example test is not actually a command (binary) on the system; it is a built-in shell function to bash. Thus, the following would not work:

service {
  check {
    type    = "script"
    command = "test -f /tmp/file.txt" # THIS IS NOT CORRECT
  }
}

Nomad will attempt to find an executable named test on your system, but it does not exist. It is actually just a function of bash. Additionally, it is not possible to specify the arguments in a single string. Here is the correct solution:

service {
  check {
    type    = "script"
    command = "/bin/bash"
    args    = ["-c", "test -f /tmp/file.txt"]
  }
}

The command is actually /bin/bash, since that is the actual process we are running. The arguments to that command are the script itself, which each argument provided as a value to the args array.

HTTP Health Check

This example shows a service with an HTTP health check. This will query the service on the IP and port registered with Nomad at /_healthz every 5 seconds, giving the service a maximum of 2 seconds to return a response, and include an Authorization header. Any non-2xx code is considered a failure.

service {
  check {
    type     = "http"
    port     = "lb"
    path     = "/_healthz"
    interval = "5s"
    timeout  = "2s"
    header {
      Authorization = ["Basic ZWxhc3RpYzpjaGFuZ2VtZQ=="]
    }
  }
}

Multiple Health Checks

This example shows a service with multiple health checks defined. All health checks must be passing in order for the service to register as healthy.

service {
  check {
    type     = "http"
    port     = "lb"
    path     = "/_healthz"
    interval = "5s"
    timeout  = "2s"
  }

  check {
    type     = "http"
    protocol = "https"
    port     = "lb"
    path     = "/_healthz"
    interval = "5s"
    timeout  = "2s"
    method   = "POST"
  }

  check {
    type     = "script"
    command  = "/usr/local/bin/pg-tools"
    args     = ["verify", "database" "prod", "up"]
    interval = "5s"
    timeout  = "2s"
  }
}

Using Driver Address Mode

The Docker and rkt drivers support the driver setting for the address_mode parameter in both service and check stanzas. The driver address mode allows advertising and health checking the IP and port assigned to a task by the driver. This way if you're using a network plugin like Weave with Docker, you can advertise the Weave address in Consul instead of the host's address.

For example if you were running the example Redis job in an environment with Weave but Consul was running on the host you could use the following configuration:

job "example" {
  datacenters = ["dc1"]
  group "cache" {

    task "redis" {
      driver = "docker"

      config {
        image = "redis:3.2"
        network_mode = "weave"
        port_map {
          db = 6379
        }
      }

      resources {
        cpu    = 500 # 500 MHz
        memory = 256 # 256MB
        network {
          mbits = 10
          port "db" {}
        }
      }

      service {
        name = "weave-redis"
        port = "db"
        check {
          name     = "host-redis-check"
          type     = "tcp"
          interval = "10s"
          timeout  = "2s"
        }
      }
    }
  }
}

No explicit address_mode required!

Services default to the auto address mode. When a Docker network mode other than "host" or "bridge" is used, services will automatically advertise the driver's address (in this case Weave's). The service will advertise the container's port: 6379.

However since Consul is often run on the host without access to the Weave network, check stanzas default to host address mode. The TCP check will run against the host's IP and the dynamic host port assigned by Nomad.

Note that the check still inherits the service stanza's db port label, but each will resolve the port label according to their address mode.

If Consul has access to the Weave network the job could be configured like this:

job "example" {
  datacenters = ["dc1"]
  group "cache" {

    task "redis" {
      driver = "docker"

      config {
        image = "redis:3.2"
        network_mode = "weave"
        # No port map required!
      }

      resources {
        cpu    = 500 # 500 MHz
        memory = 256 # 256MB
        network {
          mbits = 10
        }
      }

      service {
        name = "weave-redis"
        port = 6379
        address_mode = "driver"
        check {
          name     = "host-redis-check"
          type     = "tcp"
          interval = "10s"
          timeout  = "2s"
          port     = 6379
          
          address_mode = "driver"
        }
      }
    }
  }
}

In this case Nomad doesn't need to assign Redis any host ports. The service and check stanzas can both specify the port number to advertise and check directly since Nomad isn't managing any port assignments.

---

¹ Script checks are not supported for the qemu driver since the Nomad client does not have access to the file system of a task for that driver.