This post focuses on me being lazy. In the previous post, I talked about building a custom image and posting it to the Docker Hub. I have also talked about creating a Git repo and storing everything in it thus far. What if we could make a commit rebuild our image for us? As luck would have it, you can do this!

This post is going to focus on making that very simple change to your Docker Hub repository so that every commit causes the image to be rebuilt to the latest. How fun!

Connecting Docker Hub to Your Git Account

The major thing to accomplish here is configuring Docker Hub to monitor Git. In order to do that, you’ll need to first sign into your Docker Hub account. This should bring you to the main page where you see the list of repos you maintain:

Enabling Automatic Builds in Docker Hub

With Docker Hub and GitHub connected, the next step is to tell Docker Hub which repo to use and where the Dockerfile is located. In order to do that, go back to your repo and once again, click on the Build link. Within the Build screen, again, click on the Link to GitHub button. This time, the button should say “Connected” on it as shown below:

Now that we have everything connected and working, let’s see if we can do a commit to our repo and confirm that the commit makes a build trigger. Let’s just make a simple change and no longer expose port 443 from for the image:

FROM ubuntu
  
 MAINTAINER Scott Algatt
  
 RUN apt-get update 
     && apt-get install -y nginx libnginx-mod-http-lua libnginx-mod-http-subs-filter software-properties-common
     && add-apt-repository -y universe 
     && add-apt-repository -y ppa:certbot/certbot 
     && apt-get update 
     && apt-get -y install certbot python-certbot-nginx 
     && apt-get clean 
     && rm -rf /var/lib/apt/lists/* /tmp/* /var/tmp/*
 COPY ./conf/nginx.conf /etc/nginx/nginx.conf
 COPY ./conf/site.conf /etc/nginx/sites-available/default
  
 EXPOSE 80
 CMD ["nginx"]

With that change, let’s do a commit and push:

$ git commit -a
 [master 0e01193] Removing port 443
  Committer: Scott <[email protected]>
  
  2 files changed, 2 deletions(-)

$ git push origin master
 Counting objects: 6, done.
 Delta compression using up to 4 threads.
 Compressing objects: 100% (6/6), done.
 Writing objects: 100% (6/6), 499 bytes | 499.00 KiB/s, done.
 Total 6 (delta 3), reused 0 (delta 0)
 remote: Resolving deltas: 100% (3/3), completed with 3 local objects.
 To github.com:algattsm/mysamplerepo.git
    1d4d448..0e01193  master -> master

After performing the commit, refresh your Build page in Docker Hub and you should see a build trigger:

Referenced File

In case you want to make sure you have the correct file, here would be the only file I referenced in this post: