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Background step settings

Use Background steps to manage dependent services that need to run for the entire lifetime of a Build stage. For example, you can set up your pipeline to run multiple background services that implement a local, multi-service app.

A Build stage with multiple services running in Background steps.

A Background step starts a service and then proceeds. For any later step that relies on the service, it is good practice to verify that the service is running before sending requests.

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  • Background steps do not support failure strategies or output variables.
  • If the pipeline runs on a VM build infrastructure, you can run the background service directly on the VM rather than in a container. To do this, leave the Container Registry and Image fields blank.
  • Depending on the stage's build infrastructure, some settings might be unavailable, optional, or located under Additional Configuration.

Name and Id​

Enter a name summarizing the step's purpose. Harness automatically assigns an Id (Entity Identifier Reference) based on the Name. You can change the Id until the step is saved; once saved, the Id is locked.

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If you are using a VM, local runner, or the Harness Cloud build infrastructure where the background step is running a container, you can use the Background step Id to call services started by Background steps in later steps, such as commands in Run steps. For example, a cURL command could call BackgroundStepId:5000 where it might otherwise call localhost:5000.

The Background step ID, pythonscript, is used in a cURL command in a Run step.

If the Background step is inside a step group, you must include step group ID, such as curl StepGroupId_BackgroundStepId:5000, even if both steps are in the same step group.

If the Background step runs directly on the host or in a Kubernetes cluster build infrastructure, do not use the step ID to reference Background steps. Instead, use localhost:host_port. For Background steps running MySQL in a Kubernetes cluster build infrastructure, you must use the IP and host port, such as 127.0.0.1:7001. For more information, go to Port Bindings.

Container Registry and Image​

Container Registry is a Harness container registry connector that connects to the container registry, such as Docker Hub, from which you want Harness to pull an image.

Image is the container image to use for the background service. The image name should include the tag, or it defaults to the latest tag if unspecified. You can use any Docker image from any Docker registry, including Docker images from private registries. Different container registries require different name formats:

  • Docker Registry: Input the name of the artifact you want to deploy, such as library/tomcat. Wildcards aren't supported. FQN is required for images in private container registries.
  • ECR: Input the FQN (fully-qualified name) of the artifact you want to deploy. Images in repos must reference a path, for example: 40000005317.dkr.ecr.us-east-1.amazonaws.com/todolist:0.2.
  • GCR: Input the FQN (fully-qualified name) of the artifact you want to deploy. Images in repos must reference a path starting with the project ID that the artifact is in, for example: us.gcr.io/playground-243019/quickstart-image:latest.

An example configuration for the Container Registry and Image fields. Note that this figure shows a Run step, but the fields are populated the same for Background steps.
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The stage's build infrastructure determines whether these fields are required or optional:

  • Kubernetes cluster build infrastructure: Container Registry and Image are always required.
  • Local runner build infrastructure: Background steps can use binaries available on the host machine. The Container Registry and Image are required if the machine doesn't have the binaries you need.
  • Self-managed AWS/GCP/Azure VM build infrastructure: Background steps can use binaries that you've made available on your build VMs. The Container Registry and Image are required if the VM doesn't have the necessary binaries. These fields are located under Optional Configuration for stages that use self-managed VM build infrastructure.
  • Harness Cloud build infrastructure: Background steps can use binaries available on Harness Cloud machines, as described in the image specifications. The Container Registry and Image are required if the machine doesn't have the binary you need. These fields are located under Optional Configuration for stages that use Harness Cloud build infrastructure.

Shell, Entry Point, and Command​

Use these fields to define the commands that you need to run in the Background step.

Shell​

Select the shell type for the commands defined in Entry Point or Command. Options include: Bash, PowerShell, Pwsh (PowerShell Core), Sh, and Python. If the step includes commands that aren't supported for the selected shell type, the build fails. Required binaries must be available on the build machine or through a specified Container Registry and Image.

Entry Point​

Supply a list of arguments in exec format. Entry Point arguments override the image ENTRYPOINT and any commands in the Command field. Enter each argument separately.

If you want to add your Entry Point arguments to the image ENTRYPOINT, include both the image ENTRYPOINT, such as docker-entrypoint.sh, and your additional arguments in Entry Point.

                    entrypoint:
                      - docker-entrypoint.sh
                      - "--mtu=1450"
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In a Kubernetes cluster build infrastructure, you can use Entry Point to override port mappings when running multiple PostgreSQL instances in Background steps.

Command​

Enter POSIX shell script commands (beyond the image ENTRYPOINT) for this step. If the step runs in a container, the commands are executed inside the container.

This Bash script example checks the Java version.

              - step:
                  ...
                  spec:
                    shell: Bash
                    command: |-
                      JAVA_VER=$(java -version 2>&1 | head -1 | cut -d'"' -f2 | sed '/^1\./s///' | cut -d'.' -f1)
                      if [[ $JAVA_VER == 17 ]]; then
                        echo successfully installed $JAVA_VER
                      else
                        exit 1
                      fi
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You can use docker-compose up to start multiple services in one Background step.

Privileged​

Select this option to run the container with escalated privileges. This is the equivalent of running a container with the Docker --privileged flag.

Report Paths​

The path to the files that store results in JUnit XML format. You can add multiple paths. If you specify multiple paths, make sure the files contain unique tests to avoid duplicates. Glob is supported.

This setting is required for commands run in the Background step to be able to publish test results.

Environment Variables​

You can inject environment variables into the step container and use them in the Command script. You must input a Name and Value for each variable.

You can reference environment variables in the Command script by name. For example, a Bash script would use $var_name or ${var_name}, and a Windows PowerShell script would use $Env:varName.

Variable values can be fixed values, runtime inputs, or expressions. For example, if the value type is expression, you can input a value that references the value of some other setting in the stage or pipeline.

Using an expression for an environment variable's value.
Stage variables

Stage variables are inherently available to steps as environment variables.

Image Pull Policy​

If the service is running in a container, you can select an option to set the pull policy for the image.

  • Always: The kubelet queries the container image registry to resolve the name to an image digest every time the kubelet launches a container. If the kubelet encounters an exact digest cached locally, it uses its cached image; otherwise, the kubelet downloads (pulls) the image with the resolved digest, and uses that image to launch the container.
  • If Not Present: The image is pulled only if it is not already present locally.
  • Never: The image is assumed to exist locally. No attempt is made to pull the image.

Port Bindings​

The host port and container port binding are similar to port mapping in Docker. Usually the ports are the same unless the default host port for the Background step is already in use by another local service or you are running multiple instances of the same service.

Depending on the Build stage's Infrastructure, some steps might run directly on VMs while other steps run in containers. The port used to communicate with a service started by a Background step depends on where the step is running. For example, assume you create a Background step with the Name and ID myloginservice. To call this service in later steps in the same stage, you use:

  • myloginservice:container_port for containerized steps, such as those running in self-managed VM build infrastructures or running Docker images.
  • localhost:host_post for steps running in a Kubernetes cluster build infrastructure or directly on the build machine (such as a service running from a binary already installed on the host machine). For steps running MySQL in a Kubernetes cluster build infrastructure, you must use 127.0.0.1:host_port.
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If your build stage uses Harness Cloud build infrastructure and you are running a Docker image in a Background step, you must specify Port Bindings if you want to reference that Background step in a later step in the pipeline (such as in a cURL command in a Run step). More more information about referencing background services in other steps, go to Name and Id.

Run as User​

If the service is running in a container, you can specify the user ID to use for all processes in the pod. For more information about how to set the value, go to Set the security context for a pod.

Set Container Resources​

The maximum memory and cores that the container can use.

  • Limit Memory: The maximum memory that the container can use. You can express memory as a plain integer or as a fixed-point number using the suffixes G or M. You can also use the power-of-two equivalents Gi and Mi. Do not include spaces when entering a fixed value. The default value is 500Mi.
  • Limit CPU: The maximum number of cores that the container can use. CPU limits are measured in CPU units. Fractional requests are allowed; for example, you can specify one hundred millicpu as 0.1 or 100m. The default is 400m. For more information, go to Resource units in Kubernetes.

Troubleshoot Background steps​

Go to the CI Knowledge Base for questions and issues related to Background steps, including: