Posts tagged: docker

  • Testing Docker images with Autotest

    For awhile now, I’ve had a docker image which blindly gets rebuilt via dockerhub every time the upstream image changes. As the docker image I’m building just pulls bits and pieces from other sources, I didn’t really have anything to unit test as part of the CI process. Since it was working fine at the time, I just left it.

    Fast-forward a few years and sure enough, one of the things I bundle into the image shipped a broken version. The docker build still succeeded, but the final image didn’t work as expected. Rather than let that happen again, I thought I should find a testing solution.

    Docker’s Autotest looked like a good fit. It can run tests on new commits, PRs and crucially on upstream image changes. However, I was a bit confused how I could use it without bloating my image with tests embedded inside. Turns out it’s really simple using a multi-stage build.

    Suppose we have the following trivial docker image, where we simploy add a dummy example-app to the alpine image.

    FROM alpine:latest
    COPY app/ /app
    WORKDIR /app
    RUN ln -s /app/example-app /usr/local/bin/example-app

    We can turn it into a multi-stage image with a testing layer.

    # Create release layer and label it
    FROM alpine:latest as release
    COPY app/ /app
    WORKDIR /app
    RUN ln -s /app/example-app /usr/local/bin/example-app
    # Create testing layer
    FROM alpine:latest as test
    COPY --from=release / /
    COPY test/ /test
    WORKDIR /test
    ENTRYPOINT ["/bin/sh", "-c"]
    CMD ["./"]
    # Output release as the final image
    FROM release

    First we build the regular image and label it release. We then build a testing layer using release as a base and add in our tests. Here we just copy in a directory containing a bash script of arbitrary tests. The only requirement is that it exits with a 0 when tests pass, or anything else when they fail.

    Finally we call FROM release to ensure that on a regular build, we only build the app without the testing layer.

    For Autotest to work, we need to create a docker-compose.test.yml file with a sut service.

    version: "3.8"
          context: .
          target: "test"

    We set the target to test so that it builds and runs the test layer from our image. We can test it locally (with a deliberate test failure):

    $ docker-compose -f docker-compose.test.yml up sut
    sut_1  | Executing tests...
    sut_1  | OK - example-app should run fine
    sut_1  | FAIL - example-app should run fine
    sut_1  | PASSED: 1 FAILED: 1
    docker-autotest-example_sut_1 exited with code 1

    Now that it works locally we just need to enable Autotest in the Dockerhub settings.

    Full example repository: Autotest-example.

    April 16, 2021 - 2 minute read - docker autotest testing
  • Monitoring home internet speeds with Smokeping and Speed Test

    I’ve been monitoring my home internet’s uptime using Smokeping docker container for awhile now. But after finally switching from ADSL to a 100Mbps connection I thought it would be a good time to start also monitoring internet speeds.

    Turns out there is an existing plugin, smokeping-speedtest for Smokeping which does the job.

    For easy setup, I created a docker image to combine the plugin and it’s dependencies and with linuxserver’s docker-smokeping image as a base.

    For configuration, I just followed the instructions and added the follwing to the Probes file.

    + speedtest
    binary = /usr/local/bin/speedtest-cli
    timeout = 300
    step = 3600
    offset = random
    pings = 3
    ++ speedtest-download
    measurement = download
    ++ speedtest-upload
    measurement = upload

    I also added a new section to my Targets file to perform speed tests against a local ISP.

    + SpeedTest
    menu = Speed Tests
    title = Speed Tests
    ++ download
    menu = Download
    title = Download
    probe = speedtest-download
    server = 2173
    measurement = download
    host =
    ++ upload
    menu = Upload
    title = Upload
    probe = speedtest-upload
    server = 2173
    measurement = upload
    host =

    The complete Dockerfile is on github and the image on Docker Hub.

    July 9, 2019 - 1 minute read - smokeping speedtest docker
  • Moving from Heroku to Dokku

    With Heroku's recent changes to their plan offerings, my hosting costs were suddenly about to increase form $0 a month to $42. To run an app 24 hrs a day, you need to be on the hobby tier ($7/month). Not really happy with that, I decided to look elsewhere.

    I had previously explored Amazon's elastic beanstalk PaaS, but this time around I wanted to try hosting my own PaaS. Dokku bills itself as being a "Docker powered mini-Heroku in around 200 lines of Bash". After reading good things about it, I decided to give it a shot on a Digitial Ocean dropet.

    October 3, 2015 - 3 minute read - node heroku dokku docker node.js paas digital-ocean ubuntu