1# Workflow features
2
3## Job containers and service containers
4
5`container:` and `services:` work as on GitHub-hosted Linux runners. The containers are created in the **sandbox's own `dockerd`**, so nothing reaches the host.
6
7- **Initialize containers** runs after "Set up job":
8  - checks the Docker API version (1.35 or newer);
9  - removes labelled leftovers;
10  - creates the network `github_network_<32 hex>`;
11  - pulls (3 tries) and starts each container;
12  - waits for service health checks.
13- Registry `credentials:` go to a private `docker --config` directory under `RUNNER_TEMP`. The password goes through stdin and is masked. The directory is removed after the pull.
14- **Stop containers** is a post step (`always()`). It prints service logs and removes containers and the network. It runs after a failure, a cancellation and a timeout.
15- `run:` steps and node actions in the job container go through `docker exec`. Values are passed in the environment of the docker process, never on the command line.
16- Node actions in a job container use the externals mounted at `/__e`. `node<N>_alpine` is used when `/etc/*release` says alpine.
17- Docker actions run as siblings on the job network.
18- Contexts `job.container.{id,network}` and `job.services.<alias>.{id,network,ports}` are set.
19- Not supported: container hooks (`ACTIONS_RUNNER_CONTAINER_HOOKS`) and the "already running in a container" refusal.
20
21Security notes:
22
23- `options:` is split into arguments and passed to `docker create` as an argument vector, never through a shell. A workflow cannot inject a second command.
24- A workflow can still pass any `docker create` flag (`--privileged`, `--pid host`, `--device`) and bind volumes, as on a self-hosted GitHub runner.
25- The sandbox contains this, not the runner. **Host paths in `volumes:` and `options:` are paths of the sandbox.**
26- The runner warns about a volume that mounts `/`.
27
28## Cancellation
29
30- The host sends a cancel request to the executor.
31- The executor signals the script's process group like the official runner: SIGINT at once, SIGTERM after 7.5 s, SIGKILL 2.5 s later.
32- Background children that keep the output pipes open are killed when the shell exits.
33- Init forwards SIGTERM and SIGINT to the executor.
34- Step `timeout-minutes` is enforced.
35
36## Annotations, summaries and masks
37
38- `::notice`, `::warning` and `::error` become annotations, with `title`, `file`, `line`, `endLine`, `col` and `endColumn`.
39- Problem matchers are supported (`add-matcher`, `remove-matcher`). Each has a 1 s timeout (`GITHUB_ACTIONS_RUNNER_ISSUE_MATCHER_TIMEOUT`) and is removed after 3 timeouts.
40- Every `##[error]` the runner writes becomes an annotation.
41- Limits: 10 annotations per level per step, messages cut at 4096 characters.
42- `GITHUB_STEP_SUMMARY` is read after each step, up to 1 MiB.
43- `::add-mask::` masks values at run time.
44- Annotations and summaries are sent only when the server lists `ci.annotations` and `ci.summaries`.
45
46Attribution for the ported code: [THIRD_PARTY.md](../THIRD_PARTY.md).