Runner defaults are not honoured when registering runner with a configuration template

Summary

Registering a runner with a configuration template results in configuration that does not respect the documented runner defaults.

Steps to reproduce

Create a minimal configuration template:

> cat config-template.toml
concurrent = 50
log_format = "text"

[[runners]]
  executor = "docker-autoscaler"
  tls-ca-file = "/etc/gitlab-runner/certs/ca.pem"
  limit = 0
  output_limit = 102400

  [runners.docker]
    image = "ubuntu:24.04"
    privileged = true
    wait_for_services_timeout = 600 # seconds

  [runners.autoscaler]
    plugin = "fleeting-plugin-aws"
    capacity_per_instance = 1
    max_use_count = 5

    [runners.autoscaler.connector_config]
      username = "ec2-user"

    [[runners.autoscaler.policy]]
      idle_count = 0
      idle_time = "5m"

Using the GitLab runner image, output the default runner configuration, then register the configuration template:

> docker run --rm -it --entrypoint bash --volume ./config-template.toml:/etc/gitlab-runner/config-template.toml docker.io/gitlab/gitlab-runner:latest
root@d2007f74d17c:/# cat /etc/gitlab-runner/config.toml
concurrent = 1
check_interval = 0
shutdown_timeout = 0

[session_server]
  session_timeout = 1800
root@d2007f74d17c:/# CI_SERVER_URL=https://gitlab.com /entrypoint register --non-interactive --template-config /etc/gitlab-runner/config-template.toml --token <redacted>
Runtime platform                                    arch=arm64 os=linux pid=17 revision=b92ee590 version=17.4.0
Running in system-mode.

Merging configuration from template file "/etc/gitlab-runner/config-template.toml"
Verifying runner... is valid                        runner=t2_wFmqRp
Runner registered successfully. Feel free to start it, but if it's running already the config should be automatically reloaded!

Configuration (with the authentication token) was saved in "/etc/gitlab-runner/config.toml"

Output the runner configuration with the merged configuration template:

root@d2007f74d17c:/# cat /etc/gitlab-runner/config.toml
concurrent = 1
check_interval = 0
connection_max_age = "15m0s"
shutdown_timeout = 0

[session_server]
  session_timeout = 1800

[[runners]]
  name = "d2007f74d17c"
  output_limit = 102400
  url = "https://gitlab.com"
  id = 41736210
  token = "<redacted>"
  token_obtained_at = 2024-10-07T20:20:17Z
  token_expires_at = 0001-01-01T00:00:00Z
  tls-ca-file = "/etc/gitlab-runner/certs/ca.pem"
  executor = "docker-autoscaler"
  [runners.custom_build_dir]
  [runners.cache]
    MaxUploadedArchiveSize = 0
    [runners.cache.s3]
    [runners.cache.gcs]
    [runners.cache.azure]
  [runners.docker]
    tls_verify = false
    image = "ubuntu:24.04"
    privileged = true
    disable_entrypoint_overwrite = false
    oom_kill_disable = false
    disable_cache = false
    volumes = ["/cache"]
    wait_for_services_timeout = 600
    shm_size = 0
    network_mtu = 0
  [runners.autoscaler]
    capacity_per_instance = 1
    max_use_count = 5
    max_instances = 0
    plugin = "fleeting-plugin-aws"
    update_interval = "0s"
    update_interval_when_expecting = "0s"
    [runners.autoscaler.connector_config]
      username = "ec2-user"
      password = ""
      key_path = ""
      use_static_credentials = false
      keepalive = "0s"
      timeout = "0s"
      use_external_addr = false

    [[runners.autoscaler.policy]]
      idle_count = 0
      idle_time = "5m0s"
      scale_factor = 0.0
      scale_factor_limit = 0

Actual behavior

The following [runners.autoscaler] properties are set:

[runners.autoscaler]
  ...
  update_interval = "0s"
  update_interval_when_expecting = "0s"
  [runners.autoscaler.connector_config]
    ...
    keepalive = "0s"
    timeout = "0s"
    ...

Expected behavior

Either the update_interval and update_interval_when_expecting properties should either be omitted, or set to the documented defaults of 1m and 2s respectively.

No defaults are documented for the keepalive and timeout values, so it's unclear if they are incorrect, but if they deviate from the defaults they should either be omitted or set to the default runner values.

Environment description

config-template.toml contents

concurrent = 50
log_format = "text"

[[runners]]
  executor = "docker-autoscaler"
  tls-ca-file = "/etc/gitlab-runner/certs/ca.pem"
  limit = 0
  output_limit = 102400

  [runners.docker]
    image = "ubuntu:24.04"
    privileged = true
    wait_for_services_timeout = 600 # seconds

  [runners.autoscaler]
    plugin = "fleeting-plugin-aws"
    capacity_per_instance = 1
    max_use_count = 5

    [runners.autoscaler.connector_config]
      username = "ec2-user"

    [[runners.autoscaler.policy]]
      idle_count = 0
      idle_time = "5m"

Used GitLab Runner version

root@d2007f74d17c:/# gitlab-runner --version
Version:      17.4.0
Git revision: b92ee590
Git branch:   17-4-stable
GO version:   go1.22.5
Built:        2024-09-19T11:11:17+0000
OS/Arch:      linux/arm64