Add documentation on container/image clean-up for self-hosted runners

[stuartleeks]

As per the discussion here, it might be useful to include documentation that discusses approaches to cleaning up the containers/images from dev container builds.

On hosted agents this isn't an issue, but on private agents this maintenance is required to avoid running out of disk space.

[alexanderilyin]

.devcontainer/devcontainer.sh

#!/usr/bin/env bash

set -euxo pipefail

DEVCONTAINER_DIR=$(dirname $0)
WORKSPACE_FOLDER=$(dirname "${DEVCONTAINER_DIR}")

function cleanup()
{
    CONTAINER_ID=$(jq -r .containerId .devcontainer/up.json)
    docker rm -f "${CONTAINER_ID}"
}

trap cleanup EXIT

devcontainer --workspace-folder "${WORKSPACE_FOLDER}" build | jq . > "${DEVCONTAINER_DIR}/build.json"
devcontainer --workspace-folder "${WORKSPACE_FOLDER}" up | jq . > "${DEVCONTAINER_DIR}/up.json"
devcontainer exec --workspace-folder "${WORKSPACE_FOLDER}" "$@"

Example

$ .devcontainer/devcontainer.sh date
…
+ devcontainer --workspace-folder . build
…
+ devcontainer --workspace-folder . up
Thu Aug 10 05:04:59 UTC 2023
…
+ docker rm -f 8c679b4f2cf01a0c4683dd0cb804a9acb627127edb34c1e9f742d8863c49250d

.devcontainer/build.json

{
  "outcome": "success",
  "imageName": [
    "vsc-lorem-ipsum-388f8b1048b835a5024f54faadc273fc158a3c9e0c84d2cc5e6397577206cca4-features"
  ]
}

.devcontainer/up.json

{
  "outcome": "success",
  "containerId": "8c679b4f2cf01a0c4683dd0cb804a9acb627127edb34c1e9f742d8863c49250d",
  "remoteUser": "vscode",
  "remoteWorkspaceFolder": "/workspaces/lorem-ipsum"
}

.gitignore

.devcontainer/build.json
.devcontainer/up.json