Docker image name is changed automatically - docker

Question

I've running several containers on my host (Ubuntu Server)
I ran docker container via a command, like below
sudo docker run -d -p 5050:80 gitname/reponame
And after I call sudo docker ps and it shows
CONTAINER ID: e404ffa2bc6b
IMAGE: gitname/reponame
COMMAND: "dotnet run --server…"
CREATED: 14 seconds ago
STATUS: Up 12 seconds
PORTS: 5050/tcp, 0.0.0.0:5050->80/tcp
NAMES: reverent_mcnulty
And in a week I run sudo docker ps again and it shows another info where IMAGE was changed and it looks like ba2486f19dc0
I don't understand why.
It's problem for me because for stopping containers I use the command:
sudo docker stop $(sudo docker ps | awk '{ print $1,$2 }' | grep gitname/reponame | awk '{print $1 }')
And it doesn't work because image name already was changed

Answer 1

Every Docker image has a unique hex ID. These IDs will be different on different systems (even docker pull of the same image), but every image has exactly one ID.
Each image has some number of tags associated with it. This could be none, or multiple. docker tag will add a tag to an existing image; docker rmi will remove a tag, and also (if there are no other tags on the image, no other images using the image as a base, and no extant containers using the image) remove the image.
It's possible to "steal" the tag from an existing image. The most obvious way to do this is with docker build:
cat >Dockerfile <<EOF
FROM busybox
COPY file.txt /
EOF
echo foo > file.txt
docker build -t foo .
docker images
# note the ID for foo:latest
echo bar > file.txt
docker build -t foo .
docker images
# note the old ID will show as foo:<none>
# note a different ID for foo:latest
An explicit docker tag can do this too. Images on Docker Hub and other repositories can change too (ubuntu:16.04 is routinely re-published with security updates), and so if you docker pull an image you already have it can cause the old image to "lose its name" in favor of a newer version of that image.
How does this interact with docker run and docker ps? docker run can remember the image tag an image was started with, but if the image no longer has that tag, it forgets that datum. That's why your docker ps output reverts to showing the hex ID of the image.
There are a couple of ways around this for your application:
If the image is one you're building yourself, always use an explicit version tag (could just be the current datestamp) both when building and running the image. Then you'll never overwrite an existing image's tag. ("Don't use :latest tags.")
Use docker run --name to keep track of which container is which, and filter based on that, not the image tag. (#quentino's suggestion from comments.)
Don't explicitly docker pull in your workflow. If you don't have an image, docker run will automatically pull it for you. This will avoid existing images getting minor updates and also will avoid existing images losing their names.