docker build using BuildKit doesn't load image by default

[haines]

docker build using BuildKit does not load the image unless I specify --load. Commands that used to work like

docker build --tag=foo .

don't work any more because although the image is built, it's not loaded and the tag is not applied.

This seems like a surprising backwards incompatibility that must surely break a lot of workflows? The docker build docs don't even mention the --load flag.

I'm using Docker Desktop for Mac 4.19.0 (106363) with Docker Engine 23.0.5. In this version, BuildKit is enabled by default in the daemon

{
  "builder": {
    "gc": {
      "defaultKeepStorage": "20GB",
      "enabled": true
    }
  },
  "experimental": false,
  "features": {
    "buildkit": true
  }
}

Without --load

$ docker build --tag=foo .
[+] Building 0.6s (4/4) FINISHED
 => [internal] load .dockerignore                                                                                                                                              0.0s
 => => transferring context: 2B                                                                                                                                                0.0s
 => [internal] load build definition from Dockerfile                                                                                                                           0.0s
 => => transferring dockerfile: 86B                                                                                                                                            0.0s
 => [internal] load metadata for docker.io/library/alpine:latest                                                                                                               0.5s
 => CACHED [1/1] FROM docker.io/library/alpine@sha256:02bb6f428431fbc2809c5d1b41eab5a68350194fb508869a33cb1af4444c9b11                                                         0.0s

With --load

$ docker build --load --tag=foo .
[+] Building 0.0s (5/5) FINISHED
 => [internal] load .dockerignore                                                                                                                                              0.0s
 => => transferring context: 2B                                                                                                                                                0.0s
 => [internal] load build definition from Dockerfile                                                                                                                           0.0s
 => => transferring dockerfile: 86B                                                                                                                                            0.0s
 => [internal] load metadata for docker.io/library/alpine:latest                                                                                                               0.0s
 => CACHED [1/1] FROM docker.io/library/alpine                                                                                                                                 0.0s
 => exporting to image                                                                                                                                                         0.0s
 => => exporting layers                                                                                                                                                        0.0s
 => => writing image sha256:900fc59097d3230c61c6c6893d111067d78521c696d0c5345ac2ec512ce68c68                                                                                   0.0s
 => => naming to docker.io/library/foo                                                                                                                                         0.0s

[crazy-max]

@haines Since Docker 23, docker build is forwarded to docker buildx build (except for WCOW, DOCKER_BUILDKIT=0 or if buildx plugin is missing): docker/cli#3314

With docker/cli#3676, if docker build is forwarded to docker buildx build it will create a local docker image, except if you have a custom builder alias or if you enforce a builder name.

Can you check that you don't have a builder name enforced in your environment (BUILDX_BUILDER) and also that your ~/.docker/config.json does not have a custom builder alias?:

$ jq '.aliases' ~/.docker/config.json
{
  "builder": "buildx"
}

You can use docker buildx uninstall to remove the alias.

Can you also post the output of docker info please? Thanks.

[haines]

Ah, I found the issue. I was looking for DOCKER_ environment variables that I might have set that would cause this, but I missed that I had added BUILDX_NO_DEFAULT_LOAD=true to my dotfiles sometime back in 2020 for reasons I can't remember 😅

Thanks for your help.

[crazy-max]

Ah, I found the issue. I was looking for DOCKER_ environment variables that I might have set that would cause this, but I missed that I had added BUILDX_NO_DEFAULT_LOAD=true to my dotfiles sometime back in 2020 for reasons I can't remember 😅

Thanks for your help.

Ah right I forgot about this env var (see also https://docs.docker.com/build/building/env-vars/).