> For the complete documentation index, see [llms.txt](https://v2.dataos.info/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://v2.dataos.info/references/dataos-resources/worker/core-concepts.md).

# Core concepts

### Replicas

`replicas` controls how many Worker instances DataOS maintains. Increase the replica count when the Worker logic can safely run in parallel.

```yaml
spec:
  replicas: 1
```

### Execution mode

`executionMode` defines how the Worker is executed by the runtime. Use `default` unless the Worker stack or platform guidance requires another mode.

```yaml
spec:
  executionMode: default
```

### Resources

Use `resources.requests` and `resources.limits` to control CPU and memory allocation for the Worker runtime.

```yaml
spec:
  resources:
    requests:
      cpu: 50m
      memory: 64Mi
    limits:
      cpu: 200m
      memory: 256Mi
```

### Stack and stackSpec

`stack` selects the runtime stack. `stackSpec` contains stack-specific configuration. For the `container` stack, provide the container image, command, and arguments.

```yaml
spec:
  stack: container
  stackSpec:
    image: docker.io/library/alpine:3.20
    command:
      - sh
    arguments:
      - -c
      - "while true; do echo heartbeat; sleep 30; done"
```

Common Worker stacks include:

* `container` for custom long-running containers
* `bento` for stream processing pipelines
* `fastfun` for sink-style background runtimes

The fields under `stackSpec` depend on the selected stack.

### Projections

Use `use.projection` when the Worker needs environment variables, Secrets, or files at runtime.

For projection syntax, template engines, data sources, and troubleshooting, see [Projections](/references/dataos-resources/secret/projections.md).

```yaml
spec:
  use:
    projection:
      projections:
        envVarsTemplate: |
          WORKER_NAME: ${{worker-name}}
          FQDN: https://${{dataos-fqdn}}
        files:
          - name: verify.py
            directory: /etc/app
            template: |
              print("verify worker")
```

### Storage

Workers can use inline disk storage or mount existing Volume Resources when a background process needs local or persistent files.

* Use `disk` when storage belongs to the Worker lifecycle.
* Use `use.volumes` when data must persist independently of the Worker.


---

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