Gerrit Primary-Replica

This set of Templates provide all the components to deploy a single Gerrit primary and a single Gerrit replica in ECS


Five templates are provided in this example:

  • cf-cluster: define the ECS cluster and the networking stack
  • cf-service-primary: define the service stack running Gerrit primary
  • cf-service-replica: define the service stack running Gerrit replica
  • cf-dns-route: define the DNS routing for the service
  • cf-dashboard: define the CloudWatch dashboard for the services

Data persistency

  • EBS volumes for:
    • Indexes
    • Caches
    • Data
    • Git repositories

Deployment type

  • Latest Gerrit version deployed using the official Docker image
  • Application deployed in ECS on a single EC2 instance


  • All the logs are forwarded to AWS CloudWatch in the LogGroup with the cluster stack name. Please refer to the general logging documentation for further information on logging.


  • Standard CloudWatch monitoring metrics for each component
  • Application level CloudWatch monitoring can be enabled as described here
  • Optionally Prometheus and Grafana stack (see here)

How to run it

0 - Prerequisites

Follow the steps described in the Prerequisites section

1 - Configuration

Please refer to the configuration docs to understand how to set up the configuration and what common configuration values are needed. On top of that, you might set the additional parameters, specific for this recipe.


Configuration values affecting deployment environment and cluster properties

  • SERVICE_PRIMARY_STACK_NAME: Optional. Name of the primary service stack. gerrit-service-primary by default.
  • SERVICE_REPLICA_STACK_NAME: Optional. Name of the replica service stack. gerrit-service-replica by default.
  • DASHBOARD_STACK_NAME : Optional. Name of the dashboard stack. gerrit-dashboard by default.
  • HTTP_PRIMARY_SUBDOMAIN: Optional. Name of the primary sub domain for HTTP traffic. gerrit-http-primary-demo by default.
  • SSH_PRIMARY_SUBDOMAIN: Optional. Name of the primary sub domain for SSH traffic. gerrit-ssh-primary-demo by default.
  • HTTP_REPLICA_SUBDOMAIN: Optional. Name of the replica sub domain for HTTP traffic. gerrit-http-replica-demo by default.
  • SSH_REPLICA_SUBDOMAIN: Optional. Name of the replica sub domain for SSH traffic. gerrit-ssh-replica-demo by default.
  • GERRIT_PRIMARY_INSTANCE_ID: Optional. Identifier for the Gerrit primary instance. “gerrit-primary-replica-PRIMARY” by default.
  • GERRIT_REPLICA_INSTANCE_ID: Optional. Identifier for the Gerrit replica instance. “gerrit-primary-replica-REPLICA” by default.
  • GERRIT_VOLUME_ID : Optional. Id of an extisting EBS volume. If empty, a new volume for Gerrit data will be created
  • GERRIT_VOLUME_SNAPSHOT_ID : Optional. Ignored if GERRIT_VOLUME_ID is not empty. Id of the EBS volume snapshot used to create new EBS volume for Gerrit data.
  • GERRIT_VOLUME_SIZE_IN_GIB: Optional. The size of the Gerrit data volume, in GiBs. 10 by default.

NOTE: if you are planning to run the monitoring stack, set the PRIMARY_MAX_COUNT value to at least 2. The resources provided by a single EC2 instance won't be enough for all the services that will be ran*

  • PROMETHEUS_SUBDOMAIN: Optional. Prometheus subdomain. For example: <AWS_PREFIX>-prometheus
  • GRAFANA_SUBDOMAIN: Optional. Grafana subdomain. For example: <AWS_PREFIX>-grafana
Shared filesystem for replicas

replicas share a data via an EFS filesystem which is mounted under the /var/gerrit/git directory. This allows git data to persist beyond the lifespan of a single instance and to be shared so that replicas can scale down and up according to needs.

  • REPLICA_FILESYSTEM_ID: Optional. An existing EFS filesystem id to mount on replicas.

    If empty, a new EFS will be created to store git data. Setting this value is required when deploying a dual-primary cluster using existing data as well as performing blue/green deployments. The nested stack will be retained when the cluster is deleted, so that existing data can be used to perform blue/green deployments.

  • REPLICA_FILESYSTEM_THROUGHPUT_MODE: Optional. The throughput mode for the file system to be created. default: bursting. More info here


Auto Scaling of replicas instances

Gerrit replicas have the ability to scale in or out automatically to accommodate to the increase or decrease of traffic. The traffic might be typically coming from build or test jobs executed by some sort of automated build pipeline.

Since they all share the same git data over EFS, replicas are immediately ready to serve traffic as soon as they come up and register behind the loadbalancer.

There is a 1 to 1 relationship between replica and EC2 instances: on each EC2 instance in the ‘replica’ ASG, runs one and only one replica task. Because of this, when specifying the capacity for replicas (minimum, desired and maximum), they will both configure for the capacity of tasks as well as the capacity of the ASG, since they always need to be in sync.

The scaling policy adds or removes capacity as required to keep the average CPU Usage (of the replica service) close to the specified target value.

Now, tasks in the provisioning state that cannot find sufficient resources on the existing instances will automatically trigger the capacity provider to scale out the replica ASG. As more EC2 instances become available, tasks in the provisioning state will get placed onto those instances, reducing the number of tasks in provisioning.

Conversely, as the average CPU usage (of the replica service) drops under the specified target value, and replica tasks get removed, the capacity provider will reduce the number of EC2 instances too.

Note that only EC2 instances that are not running any replica task will scale in.

These are the available settings:

  • REPLICA_AUTOSCALING_MIN_CAPACITY Optional. The minimum number of tasks that replicas should scale in to. This is also the minimum number of EC2 instances in the replica ASG default: 1

  • REPLICA_AUTOSCALING_DESIRED_CAPACITY Optional. The desired number of replica tasks to run. This is also the desired number of EC2 instances in the replica ASG. default: 1

  • REPLICA_AUTOSCALING_MAX_CAPACITY Optional. The maximum number of tasks that replicas should scale out to. This is also the maximum number of EC2 instances in the replica ASG default: 2

  • REPLICA_AUTOSCALING_SCALE_IN_COOLDOWN Optional. The amount of time, in seconds, after a scale-in activity completes before another scale-in activity can start default: 300 seconds

  • REPLICA_AUTOSCALING_SCALE_OUT_COOLDOWN Optional. The amount of time, in seconds, to wait for a previous scale-out activity to take effect default: 300 seconds

  • REPLICA_AUTOSCALING_TARGET_CPU_PERCENTAGE Optional. Aggregate CPU utilization target for auto-scaling. Auto-scaling will add or remove tasks in the replica service to be as close as possible to this value

  • REPLICA_CAPACITY_PROVIDER_TARGET Optional. The target capacity value for the capacity provider of replicas (must be > 0 and <= 100). default: 100

    Setting this value to 100 means that there will be no spare capacity allocated on the replica ASG:

    If 3 replica tasks are needed, then the ASG will adjust to have exactly 3 EC2

    Setting this value to less than 100 enables spare capacity in the ASG. For example, if you set this value to 50 the scaling policy will adjust the EC2 until it is exactly twice the number of instances needed to run all of the tasks:

    If 3 replica tasks are needed, then there ASG will adjust to 6 EC2

  • REPLICA_CAPACITY_PROVIDER_MIN_STEP_SIZE Optional. The minimum number of EC2 instances for replicas that will scale in or scale out at one time (must be >= 1 and <= 10) default: 1

  • REPLICA_CAPACITY_PROVIDER_MAX_STEP_SIZE Optional. The maximum number of EC2 instances for replicas that will scale in or scale out at one time (must be >= 1 and <= 10) default: 1

2 - Deploy

  • Create the cluster, services and DNS routing stacks:
make [AWS_REGION=a-valid-aws-region] [AWS_PREFIX=some-cluster-prefix] create-all

The optional AWS_REGION and AWS_REFIX allow you to define where it will be deployed and what it will be named.

It might take several minutes to build the stack. You can monitor the creations of the stacks in CloudFormation

  • NOTE: the creation of the cluster needs an EC2 key pair are useful when you need to connect to the EC2 instances for troubleshooting purposes. The key pair is automatically generated and stored in a pem file on the current directory. To use when ssh-ing into your instances as follow: ssh -i cluster-keys.pem ec2-user@<ec2_instance_ip>

Cleaning up

make [AWS_REGION=a-valid-aws-region] [AWS_PREFIX=some-cluster-prefix] delete-all

The optional AWS_REGION and AWS_REFIX allow you to specify exactly which stack you target for deletion.

Note that this will not delete:

  • Secrets stored in Secret Manager
  • SSL certificates
  • ECR repositories
  • Replica EFS stack
  • VPC and subnets (if created as part of this deployment, rather than externally provided)

Persistent stacks

Blue/green deployment of the primary-replica recipe requires that the blue and the green stacks are deployed within the same VPC.

In order to preserve the VPC, the IGW and the subnet upon deletion of the blue stack, the nested network cloudformation template needs to be protected from deletion.

Note that you can completely delete the stack, including explicitly retained resources such as the EFS Git filesystem, VPC and subnets, by issuing the more aggressive command:

make [AWS_REGION=a-valid-aws-region] [AWS_PREFIX=some-cluster-prefix] delete-all-including-retained-stack

Note that this will execute a prompt to confirm your choice:

* * * * WARNING * * * * this is going to completely destroy the stack, including git data.

Are you sure you want to continue? [y/N]

If you want to automate this programmatically you can just pipe the yes command to the make:

yes | make [AWS_REGION=a-valid-aws-region] [AWS_PREFIX=some-cluster-prefix] delete-all-including-retained-stack

Access your Gerrit instances

Get the URL of your Gerrit primary instance this way:

aws cloudformation describe-stacks \
  | grep -A1 '"OutputKey": "CanonicalWebUrl"' \
  | grep OutputValue \
  | cut -d'"' -f 4

Similarly for the replica:

aws cloudformation describe-stacks \
  | grep -A1 '"OutputKey": "CanonicalWebUrl"' \
  | grep OutputValue \
  | cut -d'"' -f 4

Gerrit primary instance ports:

  • HTTP 8080
  • SSH 29418

Gerrit replica instance ports:

  • HTTP 9080
  • SSH 39418


Refer to the Docker section for information on how to setup docker or how to publish images