Fun with Docker: "Release file… is not valid yet"

Today my Docker build failed on Windows because apt-get update failed because some release files were not valid yet. It said they’d be valid in about 3.5 hours. WAT.

I don’t care about your release files! Do not exit with code 100! This is not what I want to think about right now!

Spoiler: restarting my computer fixed it. 😤

This turned out to be a problem with the system time. The Ubuntu docker containers thought it was 19:30 UTC, which is like 8 hours ago. Probably five hours ago, someone updated the release files wherever apt-get calls home to. My Docker container considered that time THE FUTURE. The scary future.

Windows had the time right, 21:30 CST (which is 6 hours earlier than UTC). Ubuntu in WSL was closer; it thought it was 19:30 CST. But Docker containers were way off. This included Docker on Windows and Docker on Ubuntu.

Entertainingly, the Docker build worked on Ubuntu in WSL. I’m pretty sure that’s because I ran this same build there long ago, and Docker had the layers cached. Each line in the Dockerfile results in a layer, so Docker starts the build operation at the first line that has changed. So it didn’t even run the apt-get update.

This is one of the ways that Docker builds are not reproducible. apt-get calls out to the world, so it doesn’t do the same thing every time. When files were updated matters, and (now I know) what time your computer thinks it is matters.

Something on the internet suggested restarting the VM that Docker uses. It seems likely that Docker on WSL and Docker on Windows (in linux-container mode) are using the same VM under the hood somewhere. I don’t know how to restart that explicitly, so I restarted the computer. Now all the clocks are right (Windows, Ubuntu in WSL, and Ubuntu containers from both Docker daemons). Now the build works fine.

I’m not currently worried about running containers in production. (I just want to develop this website without installing python’s package manager locally. This is our world.) Still working in Docker challenges me to understand more about operating systems, their package managers, networking, system clocks, etc.

Docker: it puts the Ops in DevOps. That’s my day.