new entry

Author: atuttle

blog/2022/debugging-docker-production-builds.md

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+---
+title: Debugging Docker Production Builds
+date: 2022-06-29
+desc: A quick reference on how to browse the contents of a production docker image
+img: /img/2021/barrett-ward-5WQJ_ejZ7y8-unsplash.jpg
+tags:
+  - docker
+---
+
+![Shipping containers in a busy port](/img/2021/barrett-ward-5WQJ_ejZ7y8-unsplash.jpg)
+
+Photo by <a href="https://unsplash.com/@barrettward?utm_source=unsplash&utm_medium=referral&utm_content=creditCopyText">Barrett Ward</a> on <a href="https://unsplash.com/s/photos/container?utm_source=unsplash&utm_medium=referral&utm_content=creditCopyText">Unsplash</a>{class="photo-byline"}
+
+Filing this one under things that I'm writing for my future self to reference.
+
+Who among us hasn't had the experience where you're getting a bug report for a bug that you know you fixed, and it seems like your fix is just being ignored in production? (If you haven't had that experience, I envy you!)
+
+This is especially frustrating when your production environment is a Docker container running in the cloud, built by a CI/CD server. You can't exactly SSH into the server and look at the code to make sure your deploy _actually worked_. I guess you could unblock that, but it seems like the wrong reason to open up SSH ports on your production containers and probably inadvisable.
+
+Anyway, if you find yourself in this situation, here's how you can double-check what's actually inside that production container. My notes are from Amazon's AWS Elastic Container Repository (ECR) but the steps should be the same even if you're using a different service and the syntax varies.
+
+1. Log in to ECR:
+
+```bash
+aws ecr get-login-password --region us-east-1 | docker login --username AWS --password-stdin <account-id>.dkr.ecr.us-east-1.amazonaws.com
+```
+
+2. Pull the image from ECR to your local machine:
+
+```bash
+docker pull <account-id>.dkr.ecr.us-east-1.amazonaws.com/my/repo/name:tagname
+```
+
+3. Start the container locally:
+
+```bash
+docker run -it --entrypoint /bin/bash <account-id>.dkr.ecr.us-east-1.amazonaws.com/my/repo/name:tagname
+```
+
+This starts the container in interactive mode and rather than launching its usual startup command, runs, in this case, `/bin/bash` to give you a shell to browse around the container.
+
+Now you can dig around and make sure your code changes are in fact represented in the production build, where and how you expected.
+
+What should you do if the code is what you wanted it to be and the app still doesn't work?
+
+Well, friend... That remains one of life's great mysteries.