Signed-off-by: Robin Naundorf <r.naundorf@fh-muenster.de>
(cherry picked from commit 297d6c04a3)
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>
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Robin Naundorf
Sebastiaan van Stijn
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<!--[metadata]>
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aliases = ["/engine/articles/cfengine/"]
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title = "Process management with CFEngine"
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description = "Managing containerized processes with CFEngine"
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keywords = ["cfengine, process, management, usage, docker, documentation"]
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[menu.main]
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parent = "engine_admin"
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<![end-metadata]-->
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# Process management with CFEngine
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Create Docker containers with managed processes.
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Docker monitors one process in each running container and the container
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lives or dies with that process. By introducing CFEngine inside Docker
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containers, we can alleviate a few of the issues that may arise:
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- It is possible to easily start multiple processes within a
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container, all of which will be managed automatically, with the
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normal `docker run` command.
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- If a managed process dies or crashes, CFEngine will start it again
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within 1 minute.
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- The container itself will live as long as the CFEngine scheduling
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daemon (cf-execd) lives. With CFEngine, we are able to decouple the
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life of the container from the uptime of the service it provides.
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## How it works
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CFEngine, together with the cfe-docker integration policies, are
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installed as part of the Dockerfile. This builds CFEngine into our
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Docker image.
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The Dockerfile's `ENTRYPOINT` takes an arbitrary
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amount of commands (with any desired arguments) as parameters. When we
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run the Docker container these parameters get written to CFEngine
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policies and CFEngine takes over to ensure that the desired processes
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are running in the container.
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CFEngine scans the process table for the `basename` of the commands given
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to the `ENTRYPOINT` and runs the command to start the process if the `basename`
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is not found. For example, if we start the container with
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`docker run "/path/to/my/application parameters"`, CFEngine will look for a
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process named `application` and run the command. If an entry for `application`
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is not found in the process table at any point in time, CFEngine will execute
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`/path/to/my/application parameters` to start the application once again. The
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check on the process table happens every minute.
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Note that it is therefore important that the command to start your
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application leaves a process with the basename of the command. This can
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be made more flexible by making some minor adjustments to the CFEngine
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policies, if desired.
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## Usage
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This example assumes you have Docker installed and working. We will
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install and manage `apache2` and `sshd`
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in a single container.
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There are three steps:
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1. Install CFEngine into the container.
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2. Copy the CFEngine Docker process management policy into the
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containerized CFEngine installation.
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3. Start your application processes as part of the `docker run` command.
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### Building the image
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The first two steps can be done as part of a Dockerfile, as follows.
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FROM ubuntu
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MAINTAINER Eystein Måløy Stenberg <eytein.stenberg@gmail.com>
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RUN apt-get update && apt-get install -y wget lsb-release unzip ca-certificates
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# install latest CFEngine
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RUN wget -qO- http://cfengine.com/pub/gpg.key | apt-key add -
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RUN echo "deb http://cfengine.com/pub/apt $(lsb_release -cs) main" > /etc/apt/sources.list.d/cfengine-community.list
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RUN apt-get update && apt-get install -y cfengine-community
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# install cfe-docker process management policy
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RUN wget https://github.com/estenberg/cfe-docker/archive/master.zip -P /tmp/ && unzip /tmp/master.zip -d /tmp/
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RUN cp /tmp/cfe-docker-master/cfengine/bin/* /var/cfengine/bin/
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RUN cp /tmp/cfe-docker-master/cfengine/inputs/* /var/cfengine/inputs/
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RUN rm -rf /tmp/cfe-docker-master /tmp/master.zip
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# apache2 and openssh are just for testing purposes, install your own apps here
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RUN apt-get update && apt-get install -y openssh-server apache2
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RUN mkdir -p /var/run/sshd
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RUN echo "root:password" | chpasswd # need a password for ssh
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ENTRYPOINT ["/var/cfengine/bin/docker_processes_run.sh"]
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By saving this file as Dockerfile to a working directory, you can then build
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your image with the docker build command, e.g.,
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`docker build -t managed_image`.
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### Testing the container
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Start the container with `apache2` and `sshd` running and managed, forwarding
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a port to our SSH instance:
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$ docker run -p 127.0.0.1:222:22 -d managed_image "/usr/sbin/sshd" "/etc/init.d/apache2 start"
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We now clearly see one of the benefits of the cfe-docker integration: it
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allows to start several processes as part of a normal `docker run` command.
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We can now log in to our new container and see that both `apache2` and `sshd`
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are running. We have set the root password to "password" in the Dockerfile
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above and can use that to log in with ssh:
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ssh -p222 root@127.0.0.1
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ps -ef
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UID PID PPID C STIME TTY TIME CMD
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root 1 0 0 07:48 ? 00:00:00 /bin/bash /var/cfengine/bin/docker_processes_run.sh /usr/sbin/sshd /etc/init.d/apache2 start
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root 18 1 0 07:48 ? 00:00:00 /var/cfengine/bin/cf-execd -F
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root 20 1 0 07:48 ? 00:00:00 /usr/sbin/sshd
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root 32 1 0 07:48 ? 00:00:00 /usr/sbin/apache2 -k start
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www-data 34 32 0 07:48 ? 00:00:00 /usr/sbin/apache2 -k start
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www-data 35 32 0 07:48 ? 00:00:00 /usr/sbin/apache2 -k start
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www-data 36 32 0 07:48 ? 00:00:00 /usr/sbin/apache2 -k start
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root 93 20 0 07:48 ? 00:00:00 sshd: root@pts/0
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root 105 93 0 07:48 pts/0 00:00:00 -bash
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root 112 105 0 07:49 pts/0 00:00:00 ps -ef
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If we stop apache2, it will be started again within a minute by
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CFEngine.
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service apache2 status
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Apache2 is running (pid 32).
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service apache2 stop
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* Stopping web server apache2 ... waiting [ OK ]
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service apache2 status
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Apache2 is NOT running.
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# ... wait up to 1 minute...
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service apache2 status
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Apache2 is running (pid 173).
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## Adapting to your applications
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To make sure your applications get managed in the same manner, there are
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just two things you need to adjust from the above example:
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- In the Dockerfile used above, install your applications instead of
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`apache2` and `sshd`.
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- When you start the container with `docker run`,
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specify the command line arguments to your applications rather than
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`apache2` and `sshd`.
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