Mittnite - Smart init system for containers

Mittnite is a small, but smart init system designed for usage as ENTRYPOINT in container images.

It offers the following features:

• Render configuration files from templates using Go's text/template engine.
• Start processes and manage their lifecycle
• Watch configuration files and send configurable signals to processes on change
• Wait until required services are up before starting processes (currently supporting filesystem mounts, HTTP services, MySQL, Redis, AMQP and MongoDB)

Table of contents

• Getting started
  • CLI usage
    • Basic
    • Render templates and execute custom command
  • Docker
    • Build your (go) application on top of the mittnite docker-image
    • Download mittnite in your own custom Dockerfile
• Configuration
  • Directives
    • Job
    • Boot Jobs
    • File
    • Probe
  • HCL examples
    • Start a process
    • Start a process lazily on first request
    • Render a file on startup
    • Wait until a Redis connection is possible
  • More examples
• mittnitectl

Getting started

CLI usage

Basic

$ mittnite --help

Mittnite is a small, but smart init system designed for usage as `ENTRYPOINT` in container images

Usage:
  mittnite [flags]
  mittnite [command]

Available Commands:
  help        Help about any command
  renderfiles
  up
  version     Show extended information about the current version of mittnite

Flags:
  -c, --config-dir string   set directory to where your .hcl-configs are located (default "/etc/mittnite.d")
  -h, --help                help for mittnite

Use "mittnite [command] --help" for more information about a command.

Render templates and execute custom command

This will render all template files and execute the sleep 10 afterwards.

$ mittnite renderfiles sleep 10

Docker

Build your (go) application on top of the mittnite docker-image

In order to run your own static application - e.g. a golang-binary with mittnite, we recommend to inherit the mittnite docker-image and copy your stuff on top.

FROM            quay.io/mittwald/mittnite:stable
COPY            mittnite.d/ /etc/mittnite.d/
COPY            myApplication /usr/local/bin/
# ENTRYPOINT and CMD are optional, because they are inherited by parent image

Download mittnite in your own custom Dockerfile

If you'd like to use mittnite for non-static applications like node or similar, you can download the mittnite-binary from Github.

FROM        node:12-alpine
ENV         MITTNITE_VERSION="1.1.2"
RUN         wget -qO- https://github.com/mittwald/mittnite/releases/download/v${MITTNITE_VERSION}/mittnite_${MITTNITE_VERSION}_linux_x86_64.tar.gz \
                | tar xvz -C /usr/bin mittnite && \
            chmod +x /usr/bin/mittnite
COPY        mittnite.d/ /etc/mittnite.d/
ENTRYPOINT  ["/usr/bin/mittnite"]
CMD         ["up","--config-dir", "/etc/mittnite.d"]

Configuration

The directory specified with --config-dir, or the shorthand -c, can contain any number of .hcl configuration files.

All files in that directory are loaded by mittnite on startup and can contain any of the configuration directives.

Directives

Job

A Job describes a runnable process that should be started by mittnite on startup.

A Job consists of a command and (optional) args. When a process started by a Job fails, it will be restarted for a maximum of maxAttempts attempts. If it fails for more than maxAttempts time, mittnite itself will terminate to allow your container runtime to handle the failure.

job "foo" {
  command = "/usr/local/bin/foo"
  args = ["bar"]
  maxAttempts = 3
  canFail = false
  workingDirectory = "/some/path"
}

You can append a custom environment to the process by setting env:

job "foo" {
  command = "/usr/local/bin/foo"
  args = ["bar"]
  env = ["ENABLED=1", "BAR=\"BAZ\""]
  maxAttempts = 3
  canFail = false
}

To redirect the output of a job to a separate file, stdout and/or stderr can be specified:

job "foo" {
  command = "/usr/local/bin/foo"
  args = ["bar"]
  stdout = "/tmp/foo.log"
  stderr = "/tmp/foo-errors.log"
}

You can configure a Job to watch files and to send a signal to the managed process if that file changes. This can be used, for example, to send a SIGHUP to a process to reload its configuration file when it changes.

job "foo" {
  // ...

  watch "/etc/conf.d/barfoo" {
    signal = 12
  }
}

If the running process cannot handle a signal to reload the configuration, the restart parameter can be set to true. In this case the specified signal will be sent to gracefully terminate the process and restart it afterwards:

job "foo" {
  // ...

  watch "/etc/conf.d/barfoo" {
    signal = 15 # SIGTERM
    restart = true
  }
}

In addition, it is possible to execute a command before and/or after signaling. This command should not modify the file being watched, otherwise the watcher might enter an infinite loop.

job "foo" {
  // ...

  watch "/etc/conf.d/barfoo" {
    signal = 12

    preCommand {
      command = "echo"
      args = ["before"]
    }

    postCommand {
      command = "echo"
      args = ["after"]
    }
  }
}

You can also configure a Job to start its process only on the first incoming request (a bit like systemd's socket activation). In order to configure this, you need a listener and a lazy configuration:

job "foo" {
  command = "http-server"
  args = ["-p8081", "-a127.0.0.1"]

  lazy {
    spinUpTimeout = "5s"
    coolDownTimeout = "15m"
  }

  listen "0.0.0.0:8080" {
    forward = "127.0.0.1:8081"
  }
}

The listen block will instruct mittnite itself to listen on the specified address; each connection accepted on that port will be forwarded to the address specified by forward (NOTE: mittnite will do some simple layer-4 forwarding; if your upstream service depends on working with the actual client IP addresses, you'll only see the local IP address).

If there is a lazy block present, the process itself will only be started when the first connection is opened. If the process takes some time to start up, the connection will be held for that time (the client will not notice any of this, except for the time the process needs to spin up). mittnite will wait for a duration of at most .lazy.spinUpTimeout for the process to accept connection; if this timeout is exceeded, the client connection will be closed.

When no connections have been active for a duration of at least .lazy.coolDownTimeout, mittnite will terminate the process again.

Boot Jobs

Boot jobs are "special" jobs that are executed before regular job definitions. Boot jobs are required to run to completion before any regular jobs are started.

boot "setup" {
  command = "/bin/bash"
  args = ["/init-script.sh"]
  timeout = "30s"
  env = [
    "FOO=bar"
  ]
}

File

Possible directives to use in a file definition.

file "/path/to/file.txt" {
  from = "examples/test.d/test.txt.tpl"
  params = {
    foo = "bar"
  }
}

file "/path/to/second_file.txt" {
  from = "examples/test.d/second_test.txt.tpl"
  overwrite = false
  params = {
    foo = "bar"
  }
}

Files are rendered using Golang's text rendering engine. The rendering capabilities have been enhanced with sprig functions. The env function has been removed as environment variables can be accessed via the Env template variable.

some.param = {{ .Params.foo | default "bac" }}
some.env = {{ .Env.USER | upper }}
secret = {{ randAlphaNum 16 }}

Probe

Possible directives to use in a probe definition.

probe "probe-name" {
  wait = true

  redis {
    host = {
      hostname = "localhost"
      port = 6379
    }
    password = ""
  }
  
  smtp {
    host = {
      hostname = "localhost"
      port = 25
    }
  }

  mysql {
    host = {
      hostname = "localhost"
      port = 3306
    }
    credentials = {
      user = "foo"
      password = "bar"
    }
  }
  
  amqp {
    host = {
      hostname = "localhost"
      port = 5672
    }
    credentials = {
      user = "foo"
      password = "bar"
    }
    virtualhost = "amqp.localhost.com"
  }
  
  mongodb {
    url = "mongodb://localhost:27017/mongo"
  }
  
  http {
    scheme = "http"
    host = {
        hostname = "localhost"
        port = 8080
    }
    path = "/status"
    timeout = "5s"
  }
}

Specifying a port is optional and defaults to the services default port.

HCL examples

Start a process

job webserver {
  command = "/usr/bin/http-server"

  watch "/etc/conf.d/*.conf" {
    signal = 12 # USR2
  }
}

Start a process lazily on first request

job webserver {
  command = "/usr/bin/http-server"
  args = ["-p8081", "-a127.0.0.1"]

  lazy {
    spinUpTimeout = "5s"
    coolDownTimeout = "15m"
  }

  listen "0.0.0.0:8080" {
    forward = "127.0.0.1:8081"
  }
}

Render a file on startup

file "/etc/conf.d/test.txt" {
  from = "examples/test.d/test.txt.tpl"

  params = {
    foo = "bar"
  }
}

Wait until a Redis connection is possible

probe redis {
  wait = true
  redis {
    host = {
      hostname = "localhost"
      port = 6379
    }
  }
}

More examples

More example files can be found in the examples directory

mittnitectl

mittnitectl can be used to control the mittnite process as long as the required API is enabled (mittnite up --api). Currently, it is possible to start, stop, restart jobs and display the current status.

$ mittnitectl --help
This command can be used to control mittnite by command line.

Usage:
  mittnitectl [command]

Available Commands:
  help        Help about any command
  job         Control a job via command line
  version     Show extended information about the current version of mittnite

Flags:
      --api-address string   write mittnites process id to this file (default "unix:///tmp/mittnite/mittnite.sock")
  -h, --help                 help for mittnitectl

Use "mittnitectl [command] --help" for more information about a command.

$ mittnitectl job --help
This command can be used to control a managed job.

Usage:
  mittnitectl job [command]

Available Commands:
  list        List jobs
  logs        Get logs from job
  restart     Restart a job
  start       Start a job
  status      Show job status
  stop        Stop a job

Flags:
  -h, --help   help for job

Global Flags:
      --api-address string   write mittnites process id to this file (default "unix:///var/run/mittnite.sock")

Use "mittnitectl job [command] --help" for more information about a command.

job

To control a job, it must have set the controllable flag:

job webserver {
  # ...
  controllable = true
  # ...
}