Tyler Smith

Blast off: my first Dockerized app is in production

It finally happened. One pipeline. Seven stages. Four containers. One production server. The site is live at sacmusic.com

Problems with ARGs

My main goal today was optimizing my containers for production. I managed to cut the size of my Node container in half using a multi-stage build.

I wanted to fix the jankiness I created with Django's static assets yesterday at the build step. I started by splitting my one build command into two commands in my Jenkinsfile, with the first command building the front-end and back-end, and the second building the webserver. I used the back-end image as a stage in the webserver build and tried to grab the files from there.

I tried the following in my Dockerfile, but Docker threw a fit:

FROM backend:${BUILD_TAG} as backend_assets

Docker returned the following error:

invalid reference format

I had passed the BUILD_TAG in as an environment variable, and my syntax looked like the documentation.

It turns out that Dockerfiles don't give a damn about your environment variables. For build time variables, you must declare them with the ARG keyword within the Dockerfile. Additionally, you must pass them in with the --build-args flag in the CLI.

The build command ended up looking like the following:

docker-compose --build-arg BUILD_TAG=$BUILD_TAG build webserver

And here is what went in the Dockerfile:


FROM tylerlwsmith/sacmusic-backend:${BUILD_TAG} AS backend

With this, I was able to use a multistage build to get the static assets from the back-end image into the webserver image. I fixed some pipeline issues, switched the DNS, installed an SSL certificate with certbot and the site was launched 🚀

Google broke

I ran into a strange bug after launch: my Google maps would load if it were a fresh page, but wouldn't load if I navigated to a page with a map on it. I knew there was something going wrong on the client.

I spent over an hour tracking it down, but it was those pesky ARGs again. Environment variables aren't available at build time, so I had to explicitly pass those in as ARGs then bind them to environment variables in the Dockerfile.

Next steps

Like any time I finish a project, it feels anticlimactic. Maybe I need other hobbies.

I think my next step should be getting Jenkins off of my local machine and on to a server. I have a strong desire to learn Ansible and Terraform to automate the provisioning and configuration for the site, but I think I'm going to hold off on that.

After I get Jenkins on a server, I'm going to shove this blog into containers then add full text search. Finding things on this blog is painful, and having easier integrations with Elasticsearch, MeiliSearch and Selenium was a huge part of what pushed me to learn Docker in the first place.

I also need to update SacMusic's content. Soon.