chore: update alpine base image in Dockerfile

[david-luna]

The Docker image of the agent is currently based in alpine@3.9 which is almost 3y old and have some issues related to libssl@1.1. This PR updates it to version 3.21.3.

Checklist

• Add CHANGELOG.asciidoc entry
• Commit message follows commit guidelines

[david-luna]

for reviewer: could not find a tag related to the previous sha256

curl -L -s 'https://registry.hub.docker.com/v2/repositories/library/alpine/tags?page=1&page_size=1024' | jq '.results[] | .images[] | .digest' | grep 11573

# no results, also tried with the rest of pages 

so I'm not sure abut the details of the image. In the comments above I put where I took the new sha256 and also details about the platform. Is linux; amd64 the right choice?

[trentm]

The previous tag is multi-arch image:

% docker buildx imagetools inspect alpine@sha256:115731bab0862031b44766733890091c17924f9b7781b79997f5f163be262178
Name:      docker.io/library/alpine@sha256:115731bab0862031b44766733890091c17924f9b7781b79997f5f163be262178
MediaType: application/vnd.docker.distribution.manifest.list.v2+json
Digest:    sha256:115731bab0862031b44766733890091c17924f9b7781b79997f5f163be262178

Manifests:
  Name:      docker.io/library/alpine@sha256:ab3fe83c0696e3f565c9b4a734ec309ae9bd0d74c192de4590fd6dc2ef717815
  MediaType: application/vnd.docker.distribution.manifest.v2+json
  Platform:  linux/amd64

  Name:      docker.io/library/alpine@sha256:5292cebaf695db860087c5582d340a406613891b2819092747b0388da47936c8
  MediaType: application/vnd.docker.distribution.manifest.v2+json
  Platform:  linux/arm/v6

  Name:      docker.io/library/alpine@sha256:0c6b515386fda00a17e4653f007979825f35e0086e583ddc9b91d3eda941bd1b
  MediaType: application/vnd.docker.distribution.manifest.v2+json
  Platform:  linux/arm/v7

  Name:      docker.io/library/alpine@sha256:cae6522b6a351615e547ae9222c9a05d172bc5c3240eec03072d4e1d0429a17a
  MediaType: application/vnd.docker.distribution.manifest.v2+json
  Platform:  linux/arm64/v8

  Name:      docker.io/library/alpine@sha256:c7b3e8392e08c971e98627e2bddd10c7fa9d2eae797a16bc94de9709bb9300d0
  MediaType: application/vnd.docker.distribution.manifest.v2+json
  Platform:  linux/386

  Name:      docker.io/library/alpine@sha256:fa5361fbf636d3ac50cb529dab20d810eb466de2079f5710cef4cbada29cf499
  MediaType: application/vnd.docker.distribution.manifest.v2+json
  Platform:  linux/ppc64le

  Name:      docker.io/library/alpine@sha256:97e9e9a15ef94526018e2fabfdfff14781e58b87f989d2e70543f296dcad26c6
  MediaType: application/vnd.docker.distribution.manifest.v2+json
  Platform:  linux/s390x

I'm not sure about this new one:

% docker buildx imagetools inspect alpine@sha256:1c4eef651f65e2f7daee7ee785882ac164b02b78fb74503052a26dc061c90474
Name:      docker.io/library/alpine@sha256:1c4eef651f65e2f7daee7ee785882ac164b02b78fb74503052a26dc061c90474
MediaType: application/vnd.oci.image.manifest.v1+json
Digest:    sha256:1c4eef651f65e2f7daee7ee785882ac164b02b78fb74503052a26dc061c90474

That's an "OCI" image manifest, vs. the older "Docker v2" manifest (application/vnd.docker.distribution.manifest.list.v2+json).

Ah, you selected the amd64-specific image. I think we want to use the multi-arch image manifest for the current latest Alpine v3 (per https://github.com/docker-library/repo-info/blob/master/repos/alpine/remote/3.md):

alpine@sha256:a8560b36e8b8210634f77d9f7f9efd7ffa463e380b75e2e74aff4511df3ef88c

Then perhaps change the comment above to something shorter like:

# Pin the latest Alpine 3
# https://github.com/docker-library/repo-info/blob/master/repos/alpine/remote/3.md

[trentm]

Let's also get dependabot to update this, something like this in .github/dependabot.yml:

  - package-ecosystem: "docker"
    directory: "/"
    schedule:
      interval: "weekly"

[trentm]

The previous tag is multi-arch image:

% docker buildx imagetools inspect alpine@sha256:115731bab0862031b44766733890091c17924f9b7781b79997f5f163be262178
Name:      docker.io/library/alpine@sha256:115731bab0862031b44766733890091c17924f9b7781b79997f5f163be262178
MediaType: application/vnd.docker.distribution.manifest.list.v2+json
Digest:    sha256:115731bab0862031b44766733890091c17924f9b7781b79997f5f163be262178

Manifests:
  Name:      docker.io/library/alpine@sha256:ab3fe83c0696e3f565c9b4a734ec309ae9bd0d74c192de4590fd6dc2ef717815
  MediaType: application/vnd.docker.distribution.manifest.v2+json
  Platform:  linux/amd64

  Name:      docker.io/library/alpine@sha256:5292cebaf695db860087c5582d340a406613891b2819092747b0388da47936c8
  MediaType: application/vnd.docker.distribution.manifest.v2+json
  Platform:  linux/arm/v6

  Name:      docker.io/library/alpine@sha256:0c6b515386fda00a17e4653f007979825f35e0086e583ddc9b91d3eda941bd1b
  MediaType: application/vnd.docker.distribution.manifest.v2+json
  Platform:  linux/arm/v7

  Name:      docker.io/library/alpine@sha256:cae6522b6a351615e547ae9222c9a05d172bc5c3240eec03072d4e1d0429a17a
  MediaType: application/vnd.docker.distribution.manifest.v2+json
  Platform:  linux/arm64/v8

  Name:      docker.io/library/alpine@sha256:c7b3e8392e08c971e98627e2bddd10c7fa9d2eae797a16bc94de9709bb9300d0
  MediaType: application/vnd.docker.distribution.manifest.v2+json
  Platform:  linux/386

  Name:      docker.io/library/alpine@sha256:fa5361fbf636d3ac50cb529dab20d810eb466de2079f5710cef4cbada29cf499
  MediaType: application/vnd.docker.distribution.manifest.v2+json
  Platform:  linux/ppc64le

  Name:      docker.io/library/alpine@sha256:97e9e9a15ef94526018e2fabfdfff14781e58b87f989d2e70543f296dcad26c6
  MediaType: application/vnd.docker.distribution.manifest.v2+json
  Platform:  linux/s390x

I'm not sure about this new one:

% docker buildx imagetools inspect alpine@sha256:1c4eef651f65e2f7daee7ee785882ac164b02b78fb74503052a26dc061c90474
Name:      docker.io/library/alpine@sha256:1c4eef651f65e2f7daee7ee785882ac164b02b78fb74503052a26dc061c90474
MediaType: application/vnd.oci.image.manifest.v1+json
Digest:    sha256:1c4eef651f65e2f7daee7ee785882ac164b02b78fb74503052a26dc061c90474

That's an "OCI" image manifest, vs. the older "Docker v2" manifest (application/vnd.docker.distribution.manifest.list.v2+json).

Ah, you selected the amd64-specific image. I think we want to use the multi-arch image manifest for the current latest Alpine v3 (per https://github.com/docker-library/repo-info/blob/master/repos/alpine/remote/3.md):

alpine@sha256:a8560b36e8b8210634f77d9f7f9efd7ffa463e380b75e2e74aff4511df3ef88c

Then perhaps change the comment above to something shorter like:

# Pin the latest Alpine 3
# https://github.com/docker-library/repo-info/blob/master/repos/alpine/remote/3.md