- Limitations
- Configuration
- Prerequisite software for running a Job
- Stages
- Terminating and killing executables
- Error handling
- Job response
The Custom executor
Introduced in GitLab Runner 12.1
GitLab Runner provides the Custom executor for environments that it doesn’t support natively, for example, Podman or Libvirt.
This gives you the control to create your own executor by configuring GitLab Runner to use some executable to provision, run, and clean up your environment.
The scripts you configure for the custom executor are called Drivers
.
For example, you could create a Podman driver, an LXD
driver or a Libvirt
driver.
Limitations
Below are some current limitations when using the Custom executor:
- No Interactive Web Terminal support.
Configuration
There are a few configuration keys that you can choose from. Some of them are optional.
Below is an example of configuration for the Custom executor using all available configuration keys:
[[runners]]
name = "custom"
url = "https://gitlab.com"
token = "TOKEN"
executor = "custom"
builds_dir = "/builds"
cache_dir = "/cache"
[runners.custom]
config_exec = "/path/to/config.sh"
config_args = [ "SomeArg" ]
config_exec_timeout = 200
prepare_exec = "/path/to/script.sh"
prepare_args = [ "SomeArg" ]
prepare_exec_timeout = 200
run_exec = "/path/to/binary"
run_args = [ "SomeArg" ]
cleanup_exec = "/path/to/executable"
cleanup_args = [ "SomeArg" ]
cleanup_exec_timeout = 200
graceful_kill_timeout = 200
force_kill_timeout = 200
For field definitions and which ones are required, see
[runners.custom]
section
configuration.
In addition both builds_dir
and cache_dir
inside of the
[[runners]]
are required fields.
Prerequisite software for running a Job
The user must set up the environment, including the following that must
be present in the PATH
:
- Git: Used to clone the repositories.
- Git LFS: Pulls any LFS objects that might be in the repository.
- GitLab Runner: Used to download/update artifacts and cache.
Stages
The Custom executor provides the stages for you to configure some details of the job, prepare and clean up the environment and run the job script within it. Each stage is responsible for specific things and has different things to keep in mind.
Each stage executed by the Custom executor is executed at the time a builtin GitLab Runner executor would execute them.
For each step that will be executed, specific environment variables are exposed to the executable, which can be used to get information about the specific Job that is running. All stages will have the following environment variables available to them:
- Standard CI/CD environment variables, including predefined variables.
- All environment variables provided by the Custom executor Runner host system.
- All services and their available settings.
Exposed in JSON format as
CUSTOM_ENV_CI_JOB_SERVICES
.
Both CI/CD environment variables and predefined variables are prefixed
with CUSTOM_ENV_
to prevent conflicts with system environment
variables. For example, CI_BUILDS_DIR
will be available as
CUSTOM_ENV_CI_BUILDS_DIR
.
The stages run in the following sequence:
config_exec
prepare_exec
run_exec
cleanup_exec
Services
Introduced in GitLab Runner 13.6
Services are exposed as a JSON array
as CUSTOM_ENV_CI_JOB_SERVICES
.
Example:
custom:
script:
- echo $CUSTOM_ENV_CI_JOB_SERVICES
services:
- redis:latest
- name: my-postgres:9.4
alias: pg
entrypoint: ["path", "to", "entrypoint"]
command: ["path", "to", "cmd"]
The example above will set CUSTOM_ENV_CI_JOB_SERVICES
environment variable with the following value:
[{"name":"redis:latest","alias":"","entrypoint":null,"command":null},{"name":"my-postgres:9.4","alias":"pg","entrypoint":["path","to","entrypoint"],"command":["path","to","cmd"]}]
Config
The Config stage is executed by config_exec
.
Sometimes you might want to set some settings during execution time. For
example settings a build directory depending on the project ID.
config_exec
reads from STDOUT and expects a valid JSON string with
specific keys.
For example:
#!/usr/bin/env bash
cat << EOS
{
"builds_dir": "/builds/${CUSTOM_ENV_CI_CONCURRENT_PROJECT_ID}/${CUSTOM_ENV_CI_PROJECT_PATH_SLUG}",
"cache_dir": "/cache/${CUSTOM_ENV_CI_CONCURRENT_PROJECT_ID}/${CUSTOM_ENV_CI_PROJECT_PATH_SLUG}",
"builds_dir_is_shared": true,
"hostname": "custom-hostname",
"driver": {
"name": "test driver",
"version": "v0.0.1"
},
"job_env" : {
"CUSTOM_ENVIRONMENT": "example"
}
}
EOS
Any additional keys inside of the JSON string will be ignored. If it’s not a valid JSON string the stage will fail and be retried two more times.
Parameter | Type | Required | Allowed empty | Description |
---|---|---|---|---|
builds_dir |
string | ✗ | ✗ | The base directory where the working directory of the job will be created. |
cache_dir |
string | ✗ | ✗ | The base directory where local cache will be stored. |
builds_dir_is_shared |
bool | ✗ | n/a | Defines whether the environment is shared between concurrent job or not. |
hostname |
string | ✗ | ✓ | The hostname to associate with job’s “metadata” stored by the runner. If undefined, the hostname is not set. |
driver.name |
string | ✗ | ✓ | The user-defined name for the driver. Printed with the Using custom executor... line. If undefined, no information about driver is printed. |
driver.version |
string | ✗ | ✓ | The user-defined version for the drive. Printed with the Using custom executor... line. If undefined, only the name information is printed. |
job_env |
object | ✗ | ✓ | Name-value pairs that are available through environment variables to all subsequent stages of the job execution. They are available for the driver, not the job. For details, see job_env usage. |
The STDERR
of the executable will print to the job log.
The user can set
config_exec_timeout
if they want to set a deadline for how long GitLab Runner should wait to
return the JSON string before terminating the process.
If any of the
config_exec_args
are defined, these will be added in order to the executable defined in
config_exec
. For example we have the config.toml
content below:
...
[runners.custom]
...
config_exec = "/path/to/config"
config_args = [ "Arg1", "Arg2" ]
...
GitLab Runner would execute it as /path/to/config Arg1 Arg2
.
job_env
usage
The main purpose of job_env
configuration is to pass variables to the context of custom executor driver calls
for subsequent stages of the job execution.
Let’s consider an example driver, where connection with the job execution environment requires preparing some credentials and that this operation is very expensive. Let’s say we need to connect to our local credentials provider to get a temporary SSH username and password that the custom executor can next use to connect with the job execution environment.
With Custom Executor execution flow, where each job execution stage: prepare
, multiple run
calls
and cleanup
are separate executions of the driver, the context is separate for each of them. For our credentials
resolving example, connection to the credentials provider needs to be done each time.
If this operation is expensive, we might want to do it once for a whole job execution, and then re-use the credentials
for all job execution stages. This is where the job_env
can help. With this you can connect with the provider once,
during the config_exec
call and then pass the received credentials with the job_env
. They will be next added to the
list of variables that the custom executor calls for prepare_exec
, run_exec
and cleanup_exec
are receiving. With
this, the driver instead of connecting to the credentials provider each time may just read the variables and use the
credentials that are present.
The important thing to understand is that the variables are not automaticaly available for the job itself. It fully depends on how the Custom Executor Driver is implemented and in many cases it will be not present there.
If you’re considering the job_env
setting so you can pass a set of variables to every job executed
by a particular runner, then look at the
environment
setting from [[runners]]
.
If the variables are dynamic and it’s expected that their values will change between different jobs, then you should
make sure that your driver is implemented in a way that the variables passed by job_env
will be added to the job
execution call.
Prepare
The Prepare stage is executed by prepare_exec
.
At this point, GitLab Runner knows everything about the job (where and
how it’s going to run). The only thing left is for the environment to be
set up so the job can run. GitLab Runner will execute the executable
that is specified in prepare_exec
.
This is responsible for setting up the environment (for example, creating the virtual machine or container, services or anything else). After this is done, we expect that the environment is ready to run the job.
This stage is executed only once, in a job execution.
The user can set
prepare_exec_timeout
if they want to set a deadline for how long GitLab Runner
should wait to prepare the environment before terminating the process.
The STDOUT
and STDERR
returned from this executable will print to
the job log.
If any of the
prepare_exec_args
are defined, these will be added in order to the executable defined in
prepare_exec
. For example we have the config.toml
content below:
...
[runners.custom]
...
prepare_exec = "/path/to/bin"
prepare_args = [ "Arg1", "Arg2" ]
...
GitLab Runner would execute it as /path/to/bin Arg1 Arg2
.
Run
The Run stage is executed by run_exec
.
The STDOUT
and STDERR
returned from this executable will print to
the job log.
Unlike the other stages, the run_exec
stage is executed multiple
times, since it’s split into sub stages listed below in sequential
order:
prepare_script
get_sources
restore_cache
download_artifacts
step_*
build_script
step_*
after_script
-
archive_cache
ORarchive_cache_on_failure
-
upload_artifacts_on_success
ORupload_artifacts_on_failure
cleanup_file_variables