Configuration file

Configuration file

ContainerPilot expects a configuration file with details about what services it should register, how to check their health, and what to do at startup and shutdown, among others. There are two ways to specify the ContainerPilot configuration location:

  1. An environment variable CONTAINERPILOT, pointing to the file location in the container.
  2. As an argument to ContainerPilot via the -config flag.
Examples: specifying the configuration file path
# configure via passing a file argument
$ containerpilot -config /etc/containerpilot.json5

# configure via environment variable
$ export CONTAINERPILOT=/etc/containerpilot.json5
$ containerpilot
Examples: specifying the configuration file path in a Dockerfile
# configure via environment variable
ENV CONTAINERPILOT=/etc/containerpilot.json5

The configuration file format is JSON5. If you are familiar with JSON, it is similar except that it accepts comments, fields don't need to be surrounded by quotes, and it isn't nearly as fussy about extraneous trailing commas.

Schema

The following is a completed example of the JSON5 file configuration schema, with all optional fields shown and fields annotated.

{
  consul: "localhost:8500",
  logging: {
    level: "INFO",
    format: "default",
    output: "stdout"
  },
  jobs: [
    {
      name: "app",
      exec: "/bin/app",
      restarts: "unlimited",
      port: 80,
      when: {
        // we want to start this job when the "setup" job has exited
        // with success but give up after 60 sec
        source: "setup",
        once: "exitSuccess",
        timeout: "60s"
      },
      health: {
        exec: "/usr/bin/curl --fail -s -o /dev/null http://localhost/app",
        interval: 5,
        tll: 10,
        timeout: "5s",
      },
      tags: [
        "app",
        "prod"
      ],
      interfaces: [
        "eth0",
        "eth1[1]",
        "192.168.0.0/16",
        "2001:db8::/64",
        "eth2:inet",
        "eth2:inet6",
        "inet",
        "inet6",
        "static:192.168.1.100", // a trailing comma isn't an error!
        ]
    },
    {
      // we can create a chain of "setup" events by having
      // jobs wait for other jobs to become healthy
      name: "setup",
      when: {
        source: "consul-agent",
        once: "healthy"
      },
      exec: "/usr/local/bin/preStart-script.sh",
      restart: "never"
    },
    {
      name: "preStop",
      when: {
        source: "app",
        once: "stopping"
      },
      exec: "/usr/local/bin/preStop-script.sh",
      restart: "never",
    },
    {
      name: "postStop",
      when: {
        source: "app",
        once: "stopped"
      },
      exec: "/usr/local/bin/postStop-script.sh",
    },
    {
      // a service that doesn't have a "when" field starts up on the
      // global "startup" event by default
      name: "consul-agent",
      // note we don't have a port here because we don't intend to
      // advertise one to the service discovery backend
      exec: "consul -agent -join consul",
      restart: "always"
    },
    {
      name: "consul-template",
      exec: ["consul-template", "-consul", "consul",
             "-template", "/tmp/template.ctmpl:/tmp/result"],
      restart: "always",
    },
    {
      name: "periodic-task1",
      exec: "/usr/local/bin/task.sh arg1",
      timeout: "100ms",
      when: {
        interval: "1500ms"
      }
    },
    {
      name: "reload-app",
      when: {
        source: "watch.app",
        each: "changed"
      },
      exec: "/usr/local/bin/reload-app.sh",
      timeout: "10s"
    },
    {
      name: "reload-nginx",
      when: {
        source: "watch.nginx",
        each: "changed"
      },
      exec: "/usr/local/bin/reload-nginx.sh",
      timeout: "30s"
    },
    {
      // this job will write metrics to our telemetry collector
      name: "sensor",
      exec: "/usr/local/bin/sensor.sh"
      when: {
        interval: "5s"
      }
    }
  ],
  watches: {
    {
      name: "app",
      interval: 10
    },
    {
      name: "nginx",
      interval: 30
    }
  },
  control: {
    socket: "/var/run/containerpilot.socket"
  },
  telemetry: {
    port: 9090,
    interfaces: "eth0"
    metrics: [
      {
        name: "metric_id"
        help: "help text"
        type: "counter"
      }
    ]
  }
}

Consul

ContainerPilot uses Hashicorp's Consul to register jobs in the container as services. Watches look to Consul to find out the status of other services.

Read more.

Logging

The optional logging config adjusts the output format and verbosity of ContainerPilot logs. The default behavior is to log to stdout at INFO using the go LstdFlags format.

Read more.

Jobs

Jobs are the core user-defined concept in ContainerPilot. A job is a process and rules for when to execute it, how to health check it, and how to advertise it to Consul. The rules are intended to allow for flexibility to cover nearly any type of process one might want to run.

Read more.

Watches

A watch is a configuration of a service to watch in Consul. The watch monitors the state of the service and emits events when the service becomes healthy, becomes unhealthy, or has a change in the number of instances. Note that a watch does not include a behavior; watches only emit the event so that jobs can consume that event.

Read more.

Control

Jobs often need a way to send information back to ContainerPilot to reload its own configuration, to update metrics, to put a service into maintenance mode, etc. ContainerPilot exposes a HTTP control plane that listens on a local unix socket. By default this can be found at /var/run/containerpilot.socket, and the location can be changed via the control configuration field.

Read more.

Telemetry

If a telemetry option is provided, ContainerPilot will expose a Prometheus HTTP client interface that can be used to scrape performance telemetry. The telemetry interface is advertised as a service to the discovery service similar to services configured via the jobs block. Each metric for the telemetry service will configure a collector for the Prometheus client library. Jobs can record metrics via the control socket described above. A Prometheus server can then make HTTP requests to the telemetry endpoint.

Read more.

Configuration extras

Interfaces

The interfaces parameter allows for one or more specifications to be used when searching for the advertised IP. The first specification that matches stops the search process, so they should be ordered from most specific to least specific.

  • eth0 : Match the first IPv4 address on eth0 (alias for eth0:inet)
  • eth0:inet6 : Match the first IPv6 address on eth0
  • eth0[1] : Match the 2nd IP address on eth0 (zero-based index)
  • 10.0.0.0/16 : Match the first IP that is contained within the IP Network
  • fdc6:238c:c4bc::/48 : Match the first IP that is contained within the IPv6 Network
  • inet : Match the first IPv4 Address (excluding 127.0.0.0/8)
  • inet6 : Match the first IPv6 Address (excluding ::1/128)
  • static:192.168.1.100 : Use this Address. Useful for all cases where the IP is not visible in the container

Interfaces and their IP addresses are ordered alphabetically by interface name, then by IP address (lexicographically by bytes).

Sample ordering

  • eth0 10.2.0.1 192.168.1.100
  • eth1 10.0.0.100 10.0.0.200
  • eth2 10.1.0.200 fdc6:238c:c4bc::1
  • lo ::1 127.0.0.1

Environment variables

ContainerPilot will set the following environment variables for all its child processes. Note that these environment variables are not available during configuration template parsing and rendering, because they require that the template be rendered first.

  • CONTAINERPILOT_PID: the PID of ContainerPilot itself. This will usually be '1'.
  • CONTAINERPILOT_{JOB}_IP: the IP address of every job that ContainerPilot advertises for service discovery.

Template rendering

ContainerPilot configuration has template support. If you have an environment variable such as FOO=BAR then you can use {{ .FOO }} in your configuration file or in your command arguments and it will be substituted with BAR. The CONTAINERPILOT_{JOB}_IP environment variable that is set by the services configuration is available to child processes but not to the configuration file.

Example usage in a config file

{
  consul: consul:8500,
  job: {
   exec: "/bin/setup.sh {{.URL_TO_SERVICE}} {{.API_KEY}}",
  }
}

Note: If you need more than just variable interpolation, check out the Go text/template Docs. ContainerPilot ships with the template functions from the stdlib, as well as some extensions:

default

Provides a default value if the variable is empty. For example: {{ .CONSUL | default "localhost}} would output localhost if the CONSUL env var is not set.

split and join

Split a string into parts, or join them together. For example, if we have the environment variable PARTS=a:b:c, then the following template: Hello, {{.PARTS | split ":" | join "." }}! would result in the output Hello, a.b.c!

replaceAll and regexReplaceAll

Replace a substring with another string (possibly using a regex for substring selection). For example, assume we have the environment variable NAME=Template:

  • Hello, {{.NAME | replaceAll "e" "_" }}! will output Hello, T_mplat_!
  • Hello, {{.NAME | regexReplaceAll "[epa]+" "_" }}! will output Hello, T_m_l_t_!
loop

If loop is given one integer, it will return a list that begins at zero till the integer but not including the given integer. if two integers are given it will return a list that begins from the first integer till the second integer. It works also in descending order.

  • {{ range $i := loop 5 }}{{ $i }},{{end}} will output 0,1,2,3,4,
  • {{ range $i := loop 5 8 }}{{ $i }},{{end}} will output 5,6,7,
  • {{ range $i := loop 5 1 }}{{ $i }},{{end}} will output 5,4,3,2
env

Reads string as an environment variable exposed to container pilot.

  • {{ env "MY_VAR_1" }}

If you combine loop and env you can create jobs or watches dynamically:

  watches: [
    {{ range $i := loop 0 5 -}}{{ if (env (printf "SERVICE_NAME_%d" $i)) -}}
    {
      name: "{{ (env (printf "SERVICE_NAME_%d" $i)) }}",
      interval: {{ (env (printf "SERVICE_INTERVAL_%d" $i)) | default 10 }}
    },
    {{- end }}{{- end }}
  ],