Docker use local image with buildx - docker

Question

I am building an image for a docker container running on a different architecture. As I don't have internet access all the time, I usually just pull the image when I have internet and docker uses the local image instead of pulling a new one. After I started to build the image with buildx, this does not seem to work anymore. Is there any way to tell docker to only use the local image? When I have connection, docker seems to check wherever there is a new version available but uses the local (or cached) image as I would expect it without internet connection.
$ docker image ls
ros galactic bac817d14f26 5 weeks ago 626MB
$ docker image inspect ros:galactic
...
"Architecture": "arm64",
"Variant": "v8",
"Os": "linux",
...
Example build command
$ docker buildx build . --platform linux/arm64
WARN[0000] No output specified for docker-container driver. Build result will only remain in the build cache. To push result image into registry use --push or to load image into docker use --load
[+] Building 0.3s (3/3) FINISHED
=> [internal] load build definition from Dockerfile 0.0s
=> => transferring dockerfile: 72B 0.0s
=> [internal] load .dockerignore 0.0s
=> => transferring context: 2B 0.0s
=> ERROR [internal] load metadata for docker.io/library/ros:galactic 0.0s
------
> [internal] load metadata for docker.io/library/ros:galactic:
------
Dockerfile:1
--------------------
1 | >>> FROM ros:galactic
2 | RUN "echo hello"
3 |
--------------------
error: failed to solve: failed to fetch anonymous token: Get "https://auth.docker.io/token?scope=repository%3Alibrary%2Fros%3Apull&service=registry.docker.io": proxyconnect tcp: dial tcp 127.0.0.1:3333: connect: connection refused

Answer 1

My workaround for this is to explicitly state the registry in the Dockerfile FROM sections, be it your own private registry or dockerhub.
For example, to use the dockerhub ubuntu:latest image, instead of just doing FROM ubuntu:latest I would write in the Dockerfile:
FROM docker.io/library/ubuntu:latest
To use myprivateregistry:5000 I would use:
FROM myprivateregistry:5000/ubuntu:latest
And also you must set --pull=false flag for the docker buildx build or DOCKER_BUILDKIT=1 docker build commands. When you have internet again you can use --pull=true again