Docker in the Real World - Ops
- 1. Docker in the Real World DAY 2 OPERATIONS
- 2. Troubleshooting • Build phase • Deployment • Runtime
- 3. Troubleshooting: Builds Sometimes an image fails partway through the build phase. It’s helpful to be able to fire up the broken image, enter the container, and troubleshoot. Some helpful things to look for are: • Dependencies: does the Dockerfile contain all the dependencies, settings, and configuration values needed to fire up the application? • Pinpoint what stage the build failed at. You can easily see this via docker history <imageName> or by looking at the output of the build command. • Are permissions set properly? • Are any imported scripts correct? For example, if you were to connect into a container and run a script, the results should match the expectations. Obviously, it’s much easier to troubleshoot an image when it’s not trying to do too much. Remember the guideline of one app / purpose per container. Small, focused containers.
- 4. Troubleshooting: Deployments Sometimes an image fails to deploy or, worse yet, deploys and breaks. Some helpful things to look for are: • Has the image been vetted out in test environments? • Has the image been deployed to a repository? • Are you referencing the proper name and tag? • Are credentials needed in order to access the image? • Image signing and policy restrictions can affect deployment as well. • Does your CI/CD pipeline have the access needed in order to pull down the image? • Is there a conflicting image locally that has the same name and tag?
- 5. Troubleshooting: Runtime Sometimes a container fails to run or, worse yet, runs but doesn’t yield good results. Some helpful things to look for are: • Does the container run properly locally? • Are any environmental variables needed for runtime being passed in correctly? • Are permissions for bound volumes set correctly on the host? • Are firewall rules in place that are adversely affecting traffic?
- 6. Troubleshooting Tools • Exec command • History command • Inspect command • Networking: nicolaka/netshoot