Phase 3 - execution environments

Introduction

Execution environments in CircleCI server are resourced in the following ways:

HashiCorp Nomad is used for scheduling jobs and running Docker jobs
- Nomad Server is installed and configured within your Kubernetes cluster and is used for scheduling jobs
- Nomad Clients are installed outside your Kubernetes cluster and are used for running jobs that are configured to use the Docker execution environment. CircleCI provides sample Terraform modules for you to reference and use to streamline the installation process if you are installing within AWS or GCP. Installing in this way also enables the use of the Nomad Autoscaler
Machine provisioner is used in AWS/GCP installations to provision resources and run jobs that are configured to use the machine execution environment, including Linux and Windows VMs, including Arm resources, if your server installation is within AWS. If you install outside AWS or GCP (that is, a local installation) you will use self-hosted runners to run VM-configured jobs.
Runner can be used for all execution environments, including macOS.

1. Nomad clients

Nomad is a workload orchestration tool that CircleCI uses to schedule (through Nomad server) and run (through Nomad clients) CircleCI jobs.

Nomad clients are installed outside of the Kubernetes cluster, while their control plane (Nomad Server) is installed within the cluster. Communication between your Nomad Clients and the Nomad control plane is secured with mTLS. The mTLS certificate, private key, and certificate authority will be output after you complete installation of the Nomad Clients.

If you are installing CircleCI server locally, rather than in AWS or GCP, see the Air-gapped docs on setting up Nomad clients.

a. Create your cluster with Terraform

CircleCI curates Terraform modules to help install Nomad clients in your chosen cloud provider. You can browse the modules in our public repository, including example Terraform config files for both AWS and GCP.

AWS cluster

You need some information about your cluster and server installation to populate the required variables for the Terraform module. A full example, as well as a full list of variables, can be found in the example AWS Terraform configuration.

Server_endpoint - This is the domain name of the CircleCI application.

Subnet ID (subnet), VPC ID (vpc_id), and DNS server (dns_server) of your cluster. Run the following commands to get the cluster VPC ID (vpcId), and subnets (subnetIds):

# Fetch VPC ID
aws eks describe-cluster --name=<cluster-name> --query "cluster.resourcesVpcConfig.vpcId" --region=<region> --output text | xargs

# Fetch Subnet IDs
aws eks describe-cluster --name=<cluster-name> --query "cluster.resourcesVpcConfig.subnetIds" --region=<region> --output text | xargs

This returns something similar to the following:

# VPC Id
vpc-02fdfff4ca

# Subnet Ids
subnet-08922063f12541f93 subnet-03b94b6fb1e5c2a1d subnet-0540dd7b2b2ddb57e subnet-01833e1fa70aa4488

Then, using the VPCID you just found, run the following command to get the CIDR Block for your cluster. For AWS, the DNS server is the third IP in your CIDR block (CidrBlock), for example your CIDR block might be 10.100.0.0/16, so the third IP would be 10.100.0.2.

aws ec2 describe-vpcs --filters Name=vpc-id,Values=<vpc-id> --query "Vpcs[].CidrBlock" --region=<region> --output text | xargs

This returns something like the following:

192.168.0.0/16

Once you have filled in the appropriate information, you can deploy your Nomad clients by running the following commands:

terraform init

terraform plan

terraform apply

After Terraform is done spinning up the Nomad client(s), it outputs the certificates and keys needed for configuring the Nomad control plane in CircleCI server. Copy them somewhere safe. The apply process usually only takes a minute.

GCP cluster

You need the following information:

The Domain name of the CircleCI application
The GCP Project you want to run Nomad clients in
The GCP Zone you want to run Nomad clients in
The GCP Region you want to run Nomad clients in
The GCP Network you want to run Nomad clients in
The GCP Subnetwork you want to run Nomad clients in

A full example, as well as a full list of variables, can be found in the example GCP Terraform configuration.

Once you have filled in the appropriate information, you can deploy your Nomad clients by running the following commands:

terraform init

terraform plan

terraform apply

After Terraform is done spinning up the Nomad client(s), it outputs the certificates and key needed for configuring the Nomad control plane in CircleCI server. Copy them somewhere safe.

b. Nomad Autoscaler configuration

Nomad can automatically scale up or down your Nomad clients, provided your clients are managed by a cloud provider’s auto scaling resource. With Nomad Autoscaler, you need to provide permission for the utility to manage your auto scaling resource and specify where it is located. CircleCI’s Nomad Terraform module can provision the permissions resources, or it can be done manually.

AWS autoscaler IAM/role

Create an IAM user or role and policy for Nomad Autoscaler. You may take one of the following approaches:

The CircleCI Nomad module creates an IAM user and outputs the keys if you set variable nomad_auto_scaler = true. You may reference the example in the link for more details. If you have already created the clients, you can update the variable and run terraform apply. The created user’s access and secret key will be available in Terraform’s output.
Create a Nomad Autoscaler IAM user manually with the IAM policy below. Then, generate an access and secret key for this user.
You may create a Role for Service Accounts for Nomad Autoscaler and attach the IAM policy below:

When using access and secret keys, you have two options for configuration:

IAM policy for Nomad Autoscaler

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Sid": "VisualEditor0",
            "Effect": "Allow",
            "Action": [
                "autoscaling:CreateOrUpdateTags",
                "autoscaling:UpdateAutoScalingGroup",
                "autoscaling:TerminateInstanceInAutoScalingGroup"
            ],
            "Resource": "<<Your Autoscaling Group ARN>>"
        },
        {
            "Sid": "VisualEditor1",
            "Effect": "Allow",
            "Action": [
                "autoscaling:DescribeScalingActivities",
                "autoscaling:DescribeAutoScalingGroups"
            ],
            "Resource": "*"
        }
    ]
}

GCP autoscaler service account

Create a service account for Nomad Autoscaler. You may take one of the following approaches:

2. Nomad servers

Now that you have successfully deployed your Nomad clients and have the permission resources, you can configure the Nomad Servers.

a. Nomad gossip encryption key

Nomad requires a key to encrypt communications. This key must be exactly 32 bytes long. CircleCI will not be able to recover the values if lost. Depending on how you prefer to manage Kubernetes Secrets, there are two options:

b. Nomad mTLS

The CACertificate, certificate and privateKey can be found in the output of the Terraform module. You may either add the mTLS cert values to your values.yaml or you may create a secret named nomad-mtls in the same namespace as your CircleCI server installation. The values must be base64 encoded.

c. Nomad Autoscaler

If you have enabled Nomad Autoscaler, also include the following section under nomad:

AWS

You created these values in the Nomad Autoscaler Configuration section.

nomad:
  ...
  auto_scaler:
    enabled: true
    scaling:
      max: <max-node-limit>
      min: <min-node-limit>

    aws:
      enabled: true
      region: "<region>"
      autoScalingGroup: "<asg-name>"

      accessKey: "<access-key>"
      secretKey: "<secret-key>"
      # or
      irsaRole: "<role-arn>"

GCP

You created these values in the Nomad Autoscaler Configuration section.

nomad:
  ...
  auto_scaler:
    enabled: true
    scaling:
      max: <max-node-limit>
      min: <min-node-limit>

    gcp:
      enabled: true
      project_id: "<project-id>"
      mig_name: "<instance-group-name>"

      region: "<region>"
      # or
      zone: "<zone>"

      workloadIdentity: "<service-account-email>"
      # or
      service_account: "<service-account-json>"

d. Helm upgrade

Apply the changes made to your values.yaml file:

namespace=<your-namespace>
helm upgrade circleci-server oci://cciserver.azurecr.io/circleci-server -n $namespace --version 4.5.5 -f <path-to-values.yaml>

e. Nomad clients validation

CircleCI has created a project called Reality Check which allows you to test your server installation. We are going to follow the project so we can verify that the system is working as expected. As you continue through the next phase, sections of Reality Check will move from red (fail) to green (pass).

Before running Reality Check, check if the Nomad servers can communicate with the Nomad clients by executing the below command.

kubectl -n <namespace> exec -it $(kubectl -n <namespace> get pods -l app=nomad-server -o name | tail -1) -- nomad node status

You should be able to see output like this:

ID        DC       Name              Class        Drain  Eligibility  Status
132ed55b  default  ip-192-168-44-29  linux-64bit  false  eligible     ready

To run Reality Check, you need to clone the repository. Depending on your GitHub setup, you can use one of the following commands:

GitHub cloud

git clone https://github.com/circleci/realitycheck.git

GitHub Enterprise

git clone https://github.com/circleci/realitycheck.git
git remote set-url origin <YOUR_GH_REPO_URL>
git push

Once you have successfully cloned the repository, you can follow it from within your CircleCI server installation. You need to set the following variables. For full instructions refer to the repository README.

Table 1. Environmental Variables
Name	Value
CIRCLE_HOSTNAME	<YOUR_CIRCLECI_INSTALLATION_URL>
CIRCLE_TOKEN	<YOUR_CIRCLECI_API_TOKEN>
CIRCLE_CLOUD_PROVIDER	< `aws`, `gcp`, or `other` >

Table 2. Contexts
Name	Environmental Variable Key	Environmental Variable Value
org-global	CONTEXT_END_TO_END_TEST_VAR	Leave blank
individual-local	MULTI_CONTEXT_END_TO_END_VAR	Leave blank

Once you have configured the environmental variables and contexts, rerun the Reality Check tests. You should see the features and resource jobs complete successfully. Your test results should look something like the following:

Screenshot showing the Reality Check project building in the CircleCI app

3. Machine provisioner

Overriding scaling options is currently not supported, but will be supported in the future.

Machine provisioner is used to configure virtual machines for jobs that run in Linux VM, Windows and Arm VM execution environments, and those that are configured to use remote Docker. Machine provisioner is unique to AWS and GCP installations because it relies on specific features of these cloud providers.

Once you have completed the server installation process you can further configure machine provisioner, including building and specifying a Windows image to give developers access to the Windows execution environment, specifying an alternative Linux machine image, and specifying a number of preallocated instances to remain spun up at all times. For more information, see the Manage Virtual Machines with machine provisioner page.

Before moving on to platform specific steps, create your firewall rules. External VMs need the networking rules described in Hardening your Cluster

AWS

Set up security group

Get the information needed to create security groups

The following command returns your VPC ID (vpcId) and CIDR Block (serviceIpv4Cidr) which you need throughout this section:

# Fetch VPC Id
aws eks describe-cluster --name=<cluster-name> --query "cluster.resourcesVpcConfig.vpcId" --region=<region> --output text | xargs

# Fetch CIDR Block
aws eks describe-cluster --name=<cluster-name> --query "cluster.kubernetesNetworkConfig.serviceIpv4Cidr" --region=<region> --output text | xargs

Create a security group

Run the following commands to create a security group for machine provisioner:

aws ec2 create-security-group --vpc-id "<VPC_ID>" --description "CircleCI machine provisioner security group" --group-name "circleci-machine-provisioner-sg"

This outputs a GroupID to be used in the next steps:

{
    "GroupId": "<VM_SECURITY_GROUP_ID>"
}

Apply the security group for SSH (If using public IP addresses for machines)

If using public IP addresses for your machine provisioner instances, run the following command to apply the security group rules so users can SSH into their jobs:
```
aws ec2 authorize-security-group-ingress --group-id "<VM_SECURITY_GROUP_ID>" --protocol tcp --port 54782 --cidr "0.0.0.0/0"
```

Set up authentication

Authenticate CircleCI with your cloud provider in one of two ways:

IAM Roles for Service Accounts (IRSA) - recommended.
IAM access keys.

The following is a summary of AWS’s Documentation on IRSA that is sufficient for configuring machine provisioner in CircleCI.

Create Identity Provider

Create an IAM OIDC Identity Provider for your EKS Cluster:
```
eksctl utils associate-iam-oidc-provider --cluster <CLUSTER_NAME> --approve
```

Get ARN

Get the OIDC provider ARN with the following command, you will need it in later steps:

aws iam list-open-id-connect-providers | grep $(aws eks describe-cluster --name <CLUSTER_NAME> --query "cluster.identity.oidc.issuer" --output text | awk -F'/' '{print $NF}')

Get URL

Get your OIDC provider URL, you will need it in later steps

aws eks describe-cluster --name <CLUSTER_NAME> --query "cluster.identity.oidc.issuer" --output text | sed -e "s/^https:\/\///"

Create role

Create the role using the command and trust policy template below, you will need the Role ARN and name in later steps:

aws iam create-role --role-name circleci-vm --assume-role-policy-document file://<TRUST_POLICY_FILE>

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Allow",
      "Principal": {
        "Federated": "<OIDC_PROVIDER_ARN>"
      },
      "Action": "sts:AssumeRoleWithWebIdentity",
      "Condition": {
        "StringEquals": {
          "<OIDC_PROVIDER_URL>:sub": "system:serviceaccount:<K8S_NAMESPACE>:machine-provisioner"
        }
      }
    }

  ]
}

Create policy

Create the policy using the command and template below. Fill in the security group ID and the VPC ID:

aws iam create-policy --policy-name circleci-vm --policy-document file://<POLICY_FILE>

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Action": "ec2:RunInstances",
      "Effect": "Allow",
      "Resource": [
        "arn:aws:ec2:*::image/*",
        "arn:aws:ec2:*::snapshot/*",
        "arn:aws:ec2:*:*:key-pair/*",
        "arn:aws:ec2:*:*:launch-template/*",
        "arn:aws:ec2:*:*:network-interface/*",
        "arn:aws:ec2:*:*:placement-group/*",
        "arn:aws:ec2:*:*:subnet/*",
        "arn:aws:ec2:*:*:security-group/<SECURITY_GROUP_ID>",
        "arn:aws:ec2:*:*:volume/*"
      ]
    },
    {
      "Action": "ec2:RunInstances",
      "Effect": "Allow",
      "Resource": "arn:aws:ec2:*:*:instance/*",
      "Condition": {
        "StringEquals": {
          "aws:RequestTag/ManagedBy": "circleci-machine-provisioner"
        }
      }
    },
    {
      "Action": [
        "ec2:Describe*"
      ],
      "Effect": "Allow",
      "Resource": "*"
    },
    {
      "Effect": "Allow",
      "Action": [
        "ec2:CreateTags"
      ],
      "Resource": "arn:aws:ec2:*:*:*/*",
      "Condition": {
        "StringEquals": {
          "ec2:CreateAction" : "RunInstances"
        }
      }
    },
    {
      "Action": [
        "ec2:CreateTags",
        "ec2:StartInstances",
        "ec2:StopInstances",
        "ec2:TerminateInstances"
      ],
      "Effect": "Allow",
      "Resource": "arn:aws:ec2:*:*:*/*",
      "Condition": {
        "StringEquals": {
          "ec2:ResourceTag/ManagedBy": "circleci-machine-provisioner"
        }
      }
    },
    {
      "Action": [
        "ec2:RunInstances",
        "ec2:StartInstances",
        "ec2:StopInstances",
        "ec2:TerminateInstances"
      ],
      "Effect": "Allow",
      "Resource": "arn:aws:ec2:*:*:subnet/*",
      "Condition": {
        "StringEquals": {
          "ec2:Vpc": "<VPC_ID>"
        }
      }
    }
  ]
}

Attach policy

Attach the policy to the role:

aws iam attach-role-policy --role-name <VM_ROLE_NAME> --policy-arn=<VM_POLICY_ARN>

Configure machine provisioner

Configure machine provisioner by adding the following to values.yaml:

If deploying in specific zone need to specify subnetwork for GCP

machine_provisioner:
  providers:
    ec2:
      enabled: true
      region: "<REGION>"
      assignPublicIP: true
      irsaRole: "<IRSA_ROLE_ARN>"
      subnets:
        - "<SUBNET_ID>"
      securityGroupId: "<SECURITY_GROUP_ID>"

Create user

Create a new user with programmatic access:
```
aws iam create-user --user-name circleci-machine-provisioner
```
Optionally, machine provisioner does support the use of a service account role in place of AWS keys. If you would prefer to use a role, follow these instructions using the policy in step 6 below. Once done, you may skip to step 9, enabling machine provisioner.

Create policy

Create a policy.json file with the following content. You should fill in the ID of the machine provisioner security group created in step 2 (MachineProvisionerSecurityGroupID) and VPC ID (vpcID) below.

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Action": "ec2:RunInstances",
      "Effect": "Allow",
      "Resource": [
        "arn:aws:ec2:*::image/*",
        "arn:aws:ec2:*::snapshot/*",
        "arn:aws:ec2:*:*:key-pair/*",
        "arn:aws:ec2:*:*:launch-template/*",
        "arn:aws:ec2:*:*:network-interface/*",
        "arn:aws:ec2:*:*:placement-group/*",
        "arn:aws:ec2:*:*:subnet/*",
        "arn:aws:ec2:*:*:security-group/<SECURITY_GROUP_ID>"
        "arn:aws:ec2:*:*:volume/*"
      ]
    },
    {
      "Action": "ec2:RunInstances",
      "Effect": "Allow",
      "Resource": "arn:aws:ec2:*:*:instance/*",
      "Condition": {
        "StringEquals": {
          "aws:RequestTag/ManagedBy": "circleci-machine-provisioner"
        }
      }
    },
    {
      "Action": [
        "ec2:Describe*"
      ],
      "Effect": "Allow",
      "Resource": "*"
    },
    {
      "Effect": "Allow",
      "Action": [
        "ec2:CreateTags"
      ],
      "Resource": "arn:aws:ec2:*:*:*/*",
      "Condition": {
        "StringEquals": {
          "ec2:CreateAction" : "RunInstances"
        }
      }
    },
    {
      "Action": [
        "ec2:CreateTags",
        "ec2:StartInstances",
        "ec2:StopInstances",
        "ec2:TerminateInstances"
      ],
      "Effect": "Allow",
      "Resource": "arn:aws:ec2:*:*:*/*",
      "Condition": {
        "StringEquals": {
          "ec2:ResourceTag/ManagedBy": "circleci-machine-provisioner"
        }
      }
    },
    {
      "Action": [
        "ec2:RunInstances",
        "ec2:StartInstances",
        "ec2:StopInstances",
        "ec2:TerminateInstances"
      ],
      "Effect": "Allow",
      "Resource": "arn:aws:ec2:*:*:subnet/*",
      "Condition": {
        "StringEquals": {
          "ec2:Vpc": "<VPC_ID>"
        }
      }
    }
  ]
}

Attach policy to user

Once you have created the policy.json file, attach it to an IAM policy and created user:

aws iam put-user-policy --user-name circleci-machine-provisioner --policy-name circleci-machine-provisioner --policy-document file://policy.json

Create an access key and secret for the user

If you have not already created them, you will need an access key and secret for the circleci-machine-provisioner user. You can create those by running the following command:
```
aws iam create-access-key --user-name circleci-machine-provisioner
```

Configure server (there are two options)

Option 1 - Add the keys to values.yaml Add the machine provisioner configuration to values.yaml.

machine_provisioner:
  providers:
    ec2:
      enabled: true
      region: "<REGION>"
      assignPublicIP: true
      accessKey: "<ACCESS-KEY>"
      secretKey: "<SECRET-KEY>"
      subnets:
        - "<SUBNET_ID>"
      securityGroupId: "<SECURITY_GROUP_ID>"

Option 2 - Create the Kubernetes Secret yourself Instead of providing the access key and secret in your values.yaml file, you may create the Kubernetes Secret yourself.
```
kubectl create secret generic machine-provisioner-secret \
  --from-literal=accessKey=<access-key> \
  --from-literal=secretKey=<secret-key>
```

GCP

You need additional information about your cluster to complete the next section. Run the following command:

gcloud container clusters describe

This command returns something like the following, which includes network, region, and other details that you need to complete the next section:

addonsConfig:
  gcePersistentDiskCsiDriverConfig:
    enabled: true
  kubernetesDashboard:
    disabled: true
  networkPolicyConfig:
    disabled: true
clusterIpv4Cidr: 10.100.0.0/14
createTime: '2021-08-20T21:46:18+00:00'
currentMasterVersion: 1.20.8-gke.900
currentNodeCount: 3
currentNodeVersion: 1.20.8-gke.900
databaseEncryption:
…

Create user

We recommend you create a unique service account to be used exclusively by machine provisioner. The Compute Instance Admin (Beta) role is broad enough to allow machine provisioner to operate. If you wish to make permissions more granular, you can use the Compute Instance Admin (beta) role documentation as reference.
```
gcloud iam service-accounts create circleci-server-vm --display-name "circleci-server-vm service account"
```
If you are deploying CircleCI server in a shared VCP, you should create this user in the project in which you intend to run your VM jobs.

Get the service account email address

gcloud iam service-accounts list --filter="displayName:circleci-server-vm service account" --format 'value(email)'

Apply role to service account

Apply the Compute Instance Admin (beta) role to the service account:

gcloud projects add-iam-policy-binding <YOUR_PROJECT_ID> --member serviceAccount:circleci-server-vm@<PROJECT_ID>.iam.gserviceaccount.com --role roles/compute.instanceAdmin --condition=None

And:

gcloud projects add-iam-policy-binding <YOUR_PROJECT_ID> --member serviceAccount:circleci-server-vm@<PROJECT_ID>.iam.gserviceaccount.com --role roles/iam.serviceAccountUser --condition=None

Enable Workload Identity for Service Account or get JSON key file

Choose one of the following options, depending on whether you are using Workload Identity.
This step is required only if you are using Workload Identities for GKE. Steps to enable Workload Identities are provided in Phase 1 - Prerequisites.

gcloud projects add-iam-policy-binding <PROJECT_ID> \ --member serviceAccount:circleci-server-vm@<PROJECT_ID>.iam.gserviceaccount.com \ --role roles/iam.workloadIdentityUser \ --condition=None gcloud iam service-accounts add-iam-policy-binding circleci-server-vm@<PROJECT_ID>.iam.gserviceaccount.com \ --role roles/iam.workloadIdentityUser \ --member "serviceAccount:<GCP_PROJECT_ID>.svc.id.goog[circleci-server/machine-provisioner]"
If you are using Workload Identities for GKE, this step is not required.

After running the following command, you should have a file named circleci-server-vm-keyfile in your local working directory. You will need this when you configure your server installation.

gcloud iam service-accounts keys create circleci-server-vm-keyfile --iam-account <YOUR_SERVICE_ACCOUNT_EMAIL>

Configure CircleCI server

When using service account keys for configuring access for the machine provisioner, there are two options.

Machine provisioner validation

Apply they changes made to your values.yaml file.

namespace=<your-namespace>
helm upgrade circleci-server oci://cciserver.azurecr.io/circleci-server -n $namespace --version 4.5.5 -f <path-to-values.yaml>

Once you have configured and deployed CircleCI server, you should validate that machine provisioner is operational. You can rerun the Reality Check project within your CircleCI installation and you should see the machine provisioner jobs complete. At this point, all tests should pass.

4. Runner

Overview

CircleCI runner does not require any additional server configuration. CircleCI server ships ready to work with runner. However, you need to create a runner and configure the runner agent to be aware of your server installation. For complete instructions for setting up runner, see the runner documentation.

Runner requires a namespace per organization. CircleCI server can have many organizations. If your company has multiple organizations within your CircleCI installation, you need to set up a runner namespace for each organization within your server installation.

Next steps

Phase 4: Post Installation