Comment on What is Docker?
folekaule@lemmy.world 1 day agoI know it’s ELI5, but this is a common misconception and will lead you astray. They do not have the same level of isolation, and they have very different purposes.
For example, containers are disposable cattle. You don’t backup containers. You backup volumes and configuration, but not containers.
Containers share the kernel with the host, so your container needs to be compatible with the host (though most dependencies are packaged with images).
For self hosting maybe the difference doesn’t matter much, but there is a difference.
fishpen0@lemmy.world 23 hours ago
A million times this. A major difference between the way most vms are run and most containers are run is:
VMs write to their own internal disk, containers should be immutable and not be able to write to their internal filesystem
You can have 100 identical containers running and if you are using your filesystem correctly only one copy of that container image is on your hard drive. You have have two nearly identical containers running and then only a small amount of the second container image (another layer) is wasting disk space
Similarly containers and VMs use memory and cpu allocations differently and they run with extremely different security and networking scopes, but that requires even more explanation and is less relevant to self hosting unless you are trying to learn this to eventually get a job in it.
chunkystyles@sopuli.xyz 13 hours ago
This doesn’t jive with my understanding. Containers cannot write to the image. The image is immutable. However, a running container can write to its filesystem, but those changes are ephemeral, and will disappear if the container stops.
fishpen0@lemmy.world 13 hours ago
This is why I said “most containers most of the time should”. It’s a bad practice to write to the inside of the container and a better practice to treat them as immutable. You can go as far as actively preventing them from writing to themselves when you build them or in certain container runtimes, but this is not usually how they work by default.
Also a container that is stopped and restarted will not lose its internal changes in most runtimes. The container needs to be deleted and recreated from the image to do that