Runners autoscale configuration
The autoscale feature was introduced in GitLab Runner 1.1.0.
Table of Contents generated with DocToc
- System requirements
- Runner configuration
- Autoscaling algorithm and parameters
IdleCountgenerate the upper limit of running machines
- Off Peak time mode configuration
- Distributed runners caching
- Distributed Docker registry mirroring
- A complete example of
- What are the supported cloud providers
Autoscale provides the ability to utilize resources in a more elastic and dynamic way.
When this feature is enabled and configured properly, builds are executed on
machines created on demand. Those machines, after the build is finished, can
wait to run the next builds or can be removed after the configured
In case of many cloud providers this helps to utilize the cost of already used
Thanks to runners being able to autoscale, your infrastructure contains only as much build instances as necessary at anytime. If you configure the Runner to only use autoscale, the system on which the Runner is installed acts as a bastion for all the machines it creates.
Below, you can see a real life example of the runners autoscale feature, tested on GitLab.com for the GitLab Community Edition project:
Each machine on the chart is an independent cloud instance, running build jobs inside of Docker containers.
To use the autoscale feature, the system which will host the Runner must have:
- GitLab Runner executable - installation guide can be found in GitLab Runner Documentation
- Docker Machine executable - installation guide can be found in Docker Machine documentation
If you need to use any virtualization/cloud providers that aren't handled by Docker's Machine internal drivers, the appropriate driver plugin must be installed. The Docker Machine driver plugin installation and configuration is out of the scope of this documentation. For more details please read the Docker Machine documentation.
In this section we will describe only the significant parameters from the autoscale feature point of view. For more configurations details please read the GitLab Runner - Installation and GitLab Runner - Advanced Configuration.
Runner global options
||integer||Limits how many jobs globally can be run concurrently. This is the most upper limit of number of jobs using all defined runners, local and autoscale. Together with
||string||To use the autoscale feature,
||integer||Limits how many jobs can be handled concurrently by this specific token. 0 simply means don't limit. For autoscale it's the upper limit of machines created by this provider (in conjunction with
Configuration parameters details can be found in GitLab Runner - Advanced Configuration - The runners.machine section.
Configuration parameters details can be found in GitLab Runner - Advanced Configuration - The runners.cache section
Additional configuration information
There is also a special mode, when you set
IdleCount = 0. In this mode,
machines are always created on-demand before each build (if there is no
available machine in Idle state). After the build is finished, the autoscaling
the same as it is described below.
The machine is waiting for the next builds, and if no one is executed, after
IdleTime period, the machine is removed. If there are no builds, there
are no machines in Idle state.
Autoscaling algorithm and parameters
The autoscaling algorithm is based on three main parameters:
We say that each machine that does not run a build is in Idle state. When
GitLab Runner is in autoscale mode, it monitors all machines and ensures that
there is always an
IdleCount of machines in Idle state.
At the same time, GitLab Runner is checking the duration of the Idle state of
each machine. If the time exceeds the
IdleTime value, the machine is
Example: Let's suppose, that we have configured GitLab Runner with the following autoscale parameters:
[[runners]] limit = 10 (...) executor = "docker+machine" [runners.machine] IdleCount = 2 IdleTime = 1800 (...)
At the beginning, when no builds are queued, GitLab Runner starts two machines
IdleCount = 2), and sets them in Idle state. Notice that we have also set
IdleTime to 30 minutes (
IdleTime = 1800).
Now, let's assume that 5 builds are queued in GitLab CI. The first 2 builds are
sent to the Idle machines of which we have two. GitLab Runner now notices that
the number of Idle is less than
0 < 2), so it starts 2 new
machines. Then, the next 2 builds from the queue are sent to those newly created
machines. Again, the number of Idle machines is less than
GitLab Runner starts 2 new machines and the last queued build is sent to one of
the Idle machines.
We now have 1 Idle machine, so GitLab Runner starts another 1 new machine to
IdleCount. Because there are no new builds in queue, those two
machines stay in Idle state and GitLab Runner is satisfied.
This is what happened: We had 2 machines, waiting in Idle state for new builds. After the 5 builds where queued, new machines were created, so in total we had 7 machines. Five of them were running builds, and 2 were in Idle state, waiting for the next builds.
The algorithm will still work in the same way; GitLab Runner will create a new
Idle machine for each machine used for the build execution until
is satisfied. Those machines will be created up to the number defined by
limit parameter. If GitLab Runner notices that there is a
limit number of
total created machines, it will stop autoscaling, and new builds will need to
wait in the build queue until machines start returning to Idle state.
In the above example we will always have two idle machines. The
applies only when we are over the
IdleCount, then we try to reduce the number
of machines to
After the build is finished, the machine is set to Idle state and is waiting
for the next builds to be executed. Let's suppose that we have no new builds in
the queue. After the time designated by
IdleTime passes, the Idle machines
will be removed. In our example, after 30 minutes, all machines will be removed
(each machine after 30 minutes from when last build execution ended) and GitLab
Runner will start to keep an
IdleCount of Idle machines running, just like
at the beginning of the example.
So, to sum up:
- We start the Runner
- Runner creates 2 idle machines
- Runner picks one build
- Runner creates one more machine to fulfill the strong requirement of always having the two idle machines
- Build finishes, we have 3 idle machines
- When one of the three idle machines goes over
IdleTimefrom the time when last time it picked the build it will be removed
- The Runner will always have at least 2 idle machines waiting for fast picking of the builds
Below you can see a comparison chart of builds statuses and machines statuses in time:
IdleCount generate the upper limit of running machines
There doesn't exist a magic equation that will tell you what to set
concurrent to. Act according to your needs. Having
IdleCount of Idle
machines is a speedup feature. You don't need to wait 10s/20s/30s for the
instance to be created. But as a user, you'd want all your machines (for which
you need to pay) to be running builds, not stay in Idle state. So you should
limit set to values that will run the maximum count of
machines you are willing to pay for. As for
IdleCount, it should be set to a
value that will generate a minimum amount of not used machines when the build
queue is empty.
Let's assume the following example:
concurrent=20 [[runners]] limit = 40 [runners.machine] IdleCount = 10
In the above scenario the total amount of machines we could have is 30. The
limit of total machines (building and idle) can be 40. We can have 10 idle
machines but the
concurrent builds are 20. So in total we can have 20
concurrent machines running builds and 10 idle, summing up to 30.
But what happens if the
limit is less than the total amount of machines that
could be created? The example below explains that case:
concurrent=20 [[runners]] limit = 25 [runners.machine] IdleCount = 10
In this example we will have at most 20 concurrent builds, and at most 25
machines created. In the worst case scenario regarding idle machines, we will
not be able to have 10 idle machines, but only 5, because the
limit is 25.
Off Peak time mode configuration
Introduced in GitLab Runner v1.7
Autoscale can be configured with the support for Off Peak time mode periods.
What is Off Peak time mode period?
Some organizations can select a regular time periods when no work is done. For example most of commercial companies are working from Monday to Friday in a fixed hours, eg. from 10am to 6pm. In the rest of the week - from Monday to Friday at 12am-9am and 6pm-11pm and whole Saturday and Sunday - no one is working. These time periods we're naming here as Off Peak.
Organizations where Off Peak time periods occurs probably don't want
to pay for the Idle machines when it's certain that no builds will be
executed in this time. Especially when
IdleCount is set to a big number.
v1.7 version of the Runner we've added the support for Off Peak
configuration. With parameters described in configuration file you can now
IdleTime values for the Off Peak time mode
How it is working?
Configuration of Off Peak is done by four parameters:
OffPeakPeriods setting contains an array of cron-style patterns defining
when the Off Peak time mode should be set on. For example:
[runners.machine] OffPeakPeriods = [ "* * 0-9,18-23 * * mon-fri *", "* * * * * sat,sun *" ]
will enable the Off Peak periods described above, so the working days from 12am to 9am and from 6pm to 11pm and whole weekend days. Machines scheduler is checking all patterns from the array and if at least one of them describes current time, then the Off Peak time mode is enabled.
You can specify the
"Australia/Sydney". If you don't,
the system setting of the host machine of every runner will be used. This
default can be stated as
OffPeakTimezone = "Local" explicitly if you wish.
When the Off Peak time mode is enabled machines scheduler use
OffPeakIdleCount instead of
IdleCount setting and
IdleTime setting. The autoscaling algorithm is not changed,
only the parameters. When machines scheduler discovers that none from
OffPeakPeriods pattern is fulfilled then it switches back to
More information about syntax of
OffPeakPeriods patterns can be found
in GitLab Runner - Advanced Configuration - The runners.machine section.
Distributed runners caching
To speed up your builds, GitLab Runner provides a cache mechanism where selected directories and/or files are saved and shared between subsequent builds.
This is working fine when builds are run on the same host, but when you start using the Runners autoscale feature, most of your builds will be running on a new (or almost new) host, which will execute each build in a new Docker container. In that case, you will not be able to take advantage of the cache feature.
To overcome this issue, together with the autoscale feature, the distributed Runners cache feature was introduced.
It uses any S3-compatible server to share the cache between used Docker hosts. When restoring and archiving the cache, GitLab Runner will query the S3 server and will download or upload the archive.
To enable distributed caching, you have to define it in
config.toml using the
[[runners]] limit = 10 executor = "docker+machine" [runners.cache] Type = "s3" ServerAddress = "s3.example.com" AccessKey = "access-key" SecretKey = "secret-key" BucketName = "runner" Insecure = false Path = "path/to/prefix" Shared = false
The S3 URLs follow the structure
To share the cache between two or more runners, set the
Shared flag to true. That will remove the runner token from the S3 URL (
runner/<runner-id>) and all configured runners will share the same cache. Remember that you can also set
Path to separate caches between runners when cache sharing is enabled.
Read how to install your own caching server.
Distributed Docker registry mirroring
To speed up builds executed inside of Docker containers, you can use the Docker registry mirroring service. This will provide a proxy between your Docker machines and all used registries. Images will be downloaded once by the registry mirror. On each new host, or on an existing host where the image is not available, it will be downloaded from the configured registry mirror.
Provided that the mirror will exist in your Docker machines LAN, the image downloading step should be much faster on each host.
To configure the Docker registry mirroring, you have to add
the configuration in
[[runners]] limit = 10 executor = "docker+machine" [runners.machine] (...) MachineOptions = [ (...) "engine-registry-mirror=http://10.11.12.13:12345" ]
10.11.12.13:12345 is the IP address and port where your registry mirror
is listening for connections from the Docker service. It must be accessible for
each host created by Docker Machine.
Read how to install your own Docker registry server.
A complete example of
config.toml below uses the
digitalocean Docker Machine driver:
concurrent = 50 # All registered Runners can run up to 50 concurrent builds [[runners]] url = "https://gitlab.com" token = "RUNNER_TOKEN" # Note this is different from the registration token used by `gitlab-runner register` name = "autoscale-runner" executor = "docker+machine" # This Runner is using the 'docker+machine' executor limit = 10 # This Runner can execute up to 10 builds (created machines) [runners.docker] image = "ruby:2.1" # The default image used for builds is 'ruby:2.1' [runners.machine] OffPeakPeriods = [ # Set the Off Peak time mode on for: "* * 0-9,18-23 * * mon-fri *", # - Monday to Friday for 12am to 9am and 6pm to 11pm "* * * * * sat,sun *" # - whole Saturday and Sunday ] OffPeakIdleCount = 1 # There must be 1 machine in Idle state - when Off Peak time mode is on OffPeakIdleTime = 1200 # Each machine can be in Idle state up to 1200 seconds (after this it will be removed) - when Off Peak time mode is on IdleCount = 5 # There must be 5 machines in Idle state - when Off Peak time mode is off IdleTime = 600 # Each machine can be in Idle state up to 600 seconds (after this it will be removed) - when Off Peak time mode is off MaxBuilds = 100 # Each machine can handle up to 100 builds in a row (after this it will be removed) MachineName = "auto-scale-%s" # Each machine will have a unique name ('%s' is required) MachineDriver = "digitalocean" # Docker Machine is using the 'digitalocean' driver MachineOptions = [ "digitalocean-image=coreos-stable", "digitalocean-ssh-user=core", "digitalocean-access-token=DO_ACCESS_TOKEN", "digitalocean-region=nyc2", "digitalocean-size=4gb", "digitalocean-private-networking", "engine-registry-mirror=http://10.11.12.13:12345" # Docker Machine is using registry mirroring ] [runners.cache] Type = "s3" # The Runner is using a distributed cache with Amazon S3 service ServerAddress = "s3-eu-west-1.amazonaws.com" AccessKey = "AMAZON_S3_ACCESS_KEY" SecretKey = "AMAZON_S3_SECRET_KEY" BucketName = "runners" Insecure = false
Note that the
MachineOptions parameter contains options for the
driver which is used by Docker Machine to spawn machines hosted on Digital Ocean,
and one option for Docker Machine itself (
What are the supported cloud providers
The autoscale mechanism currently is based on Docker Machine. Advanced configuration options, including virtualization/cloud provider parameters, are available at the Docker Machine documentation.