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> My own concerns revolve around how easy it will be to keep updated on RHEL patches, for example -- apparently we should be able to keep both host and app depe
by creshal 11y ago
> My own concerns revolve around how easy it will be to keep updated on RHEL patches, for example -- apparently we should be able to keep both host and app dependencies updated without much trouble, but it adds more complexity to the maintenance cycle (it seems).
That's about the "problem" with Docker – it's deceptively easy to roll out everything as its own containerized app. Updating? Not so much.
It turns Docker from a magical silver bullet into a slightly fancier way to handle reproducible deployments. Using it this way is fine, but not what Docker is marketed as by many.
- olavgg 11y agoActually its pretty easy, I just did it yesterday for my PostgreSQL container. Debian/Ubuntu example: sudo docker exec -it my_pgsql_container_name /bin/sh -c "apt-get update; apt-get -qqy upgrade; apt-get clean"
- tomaac 11y agoAnd what happens when you launch new container from the same image? You need to run apt-get/yum again. Or rebuild image.
- s_baby 11y agoThat's why you keep everything with state in a separate volume container. Attach volume to built image and that's it.
- alextgordon 11y agoYou can, if you want, mount your root as readonly so you're not tempted to modify it. Then it behaves like a Live CD.
- jeromenerf 11y agoMount data, logs, configuration, eventual extensions in the data container? For pg, there might be some migration needed when jumping from a major version to the next. Which requires both versions installed, on Debian at least.
- s_baby 11y ago>Mount data, logs, configuration, eventual extensions in the data container? Many programs have their state represented as files that are stable across versions. If you have a cluster of the same image with different states it's more efficient to move volume containers across a network. Easier to backup/upgrade too. pg is going to give you those problems whether you are using Docker or not.
- KaiserPro 11y agoand that defeats the whole selling point of docker, which is no forward config, containers do not change once shipped.
- ChrisArgyle 11y agoWorse, doing this breaks your guarantee that all environments deployed from this image will be consistent. You'll have to deploy some config management software (Puppet/Chef/Salt/Ansible) to stay on top of these changes.