# Configuring CI Using CircleCI and Nx

The `CircleCI` can track the last successful run on `main` branch and use this as a reference point for the `BASE`. The `Nx Orb` provides convenient implementation of this functionality which you can drop into you existing CI config.
To understand why knowing the last successful build is important for the affected command, check out the [in-depth explanation at Orb's docs](https://github.com/nrwl/nx-orb#background).

Below is an example of a Circle CI setup for an Nx workspace only building and testing what is affected. For more details on how the orb is used, head over to the [official docs](https://circleci.com/developer/orbs/orb/nrwl/nx).

```yaml
version: 2.1
orbs:
  nx: nrwl/nx@1.5.1
jobs:
  main:
    docker:
      - image: cimg/node:lts-browsers
    steps:
      - checkout
      - run: npm ci
      - nx/set-shas

      - run: npx nx workspace-lint
      - run: npx nx format:check
      - run: npx nx affected --base=$NX_BASE --head=$NX_HEAD --target=lint --parallel=3
      - run: npx nx affected --base=$NX_BASE --head=$NX_HEAD --target=test --parallel=3 --configuration=ci
      - run: npx nx affected --base=$NX_BASE --head=$NX_HEAD --target=build --parallel=3
workflows:
  build:
    jobs:
      - main
```

The `pr` and `main` jobs implement the CI workflow.

### Using CircleCI on private repository

To use the [Nx Orb](https://github.com/nrwl/nx-orb) with a private repository on your main branch, you need to grant the orb access to your CircleCI API. You can do this by creating an environment variable called `CIRCLE_API_TOKEN` in the context or the project.

{% callout type="warning" title="Caution" %}
It should be a user token, not project token.
{% /callout %}

{% nx-cloud-section %}

## Distributed CI with Nx Cloud

In order to use distributed task execution, we need to start agents and set the `NX_CLOUD_DISTRIBUTED_EXECUTION` flag to `true`.

Read more about the [Distributed CI setup with Nx Cloud](/recipes/ci/ci-setup#distributed-ci-with-nx-cloud).

```yaml
version: 2.1
orbs:
  nx: nrwl/nx@1.5.1
jobs:
  agent:
    docker:
      - image: cimg/node:lts-browsers
    parameters:
      ordinal:
        type: integer
    steps:
      - checkout
      - run: npm ci
      - run:
          command: npx nx-cloud start-agent
          no_output_timeout: 60m
  main:
    docker:
      - image: cimg/node:lts-browsers
    steps:
      - checkout
      - run: npm ci
      - nx/set-shas
      - run: npx nx-cloud start-ci-run --stop-agents-after="build"

      - run: npx nx-cloud record -- npx nx workspace-lint
      - run: npx nx-cloud record -- npx nx format:check
      - run: npx nx affected --base=$NX_BASE --head=$NX_HEAD --target=lint --parallel=3 & npx nx affected --base=$NX_BASE --head=$NX_HEAD --target=test --parallel=3 --configuration=ci & npx nx affected --base=$NX_BASE --head=$NX_HEAD --target=build --parallel=3
workflows:
  build:
    jobs:
      - agent:
          matrix:
            parameters:
              ordinal: [1, 2, 3]
      - main
```

You can also use our [ci-workflow generator](/packages/workspace/generators/ci-workflow) to generate the configuration file.

{% /nx-cloud-section %}
