How to Build and push with non-root users

Use the buildah plugin if you can't use the built-in Build and Push steps.

Introduction

Building with non-root users may be necessary for an organization due to security or compliance requirements. This page describes how to build and push Docker images as a non-root user, and outlines Harness options and best practices for Kubernetes-based builds.

Kaniko Builds

By default, Harness uses Kaniko to build and push images in Kubernetes cluster build infrastructure.

CHAINGUARD KANIKO FORK

The Drone Kaniko Plugin uses Chainguard's maintained Kaniko fork, ensuring continued security updates and improvements.

Kaniko does not require privileged mode (privileged: false).
Kaniko can run as non-root in many cases. Root access is only required when your Dockerfile performs privileged operations.
Security recommendation: Run Kaniko in root mode only when your Dockerfile requires privileged operations.
If your Dockerfile requires privileged operations and your policy prohibits root: Use the Buildah plugin described below.
Kaniko is recommended for most security-conscious teams as it minimizes risk by not requiring privileged pods.

WHEN TO USE ROOT MODE

Kaniko requires root mode when your Dockerfile:

Installs system packages (apt, yum, apk)
Modifies root-owned directories
Creates users or groups
Changes file ownership with chown

For Dockerfiles that don't perform these operations, consider alternatives like Buildah.

To balance security and functionality, run the pipeline stage as non-root (runAsNonRoot: true) and set runAsUser: 0 only on the Build and Push step when needed.

BuildX Builds

You may also use BuildX by enabling the CI_USE_BUILDX_ON_K8 flag via Harness Support.

BuildX requires both root user and privileged mode in Kubernetes.
This tool provides the richest feature set, but is the least restrictive in terms of privileges, and is not recommended where least-privilege is a hard requirement.

Drone Docker

You can also use drone-docker for image builds as a plugin step.

This method is generally used for backwards compatibility or in specific CI workflows.
Privilege and user requirements will be similar to Docker/BuildX (privileged and root).

Individual Step Root / Buildah Plugin

If your Kubernetes cluster build infrastructure is configured to run as non-root (runAsNonRoot: true and runAsUser: 1000), you have two options for building images:

Enable root access for individual steps (if allowed by policy): If your build infrastructure is set up for non-root execution (runAsNonRoot: true), but your security policy allows Build and Push to run as root, set Run as User to 0 for that step only. This enables only that step to run as root.
If your security policy forbids root user entirely for all steps, use the Buildah plugin running as a non-root user, with privileged mode enabled.
Use the Buildah plugin: If your policy does not allow root for any step, use the Buildah plugin in a Plugin step, and specify a non-root UID (runAsUser: 1000). Buildah can run as a non-root user (e.g., UID 1000). However, it still requires privileged mode in Kubernetes (except for some OpenShift SCC scenarios). This is due to kernel-level operations required by Buildah, even in rootless mode.
Buildah requires special configuration for OpenShift clusters (use the anyuid SCC and privileged: false). For standard Kubernetes clusters, privileged: true is required even for non-root user.
To use the Buildah plugin, your pipeline must meet these requirements:
- CI pipeline with a Build stage
- Kubernetes cluster build infrastructure set to run as non-root
- For OpenShift Buildah users: anyuid SCC is required. OpenShift SCC documentation

Add a Plugin step

At the point in your pipeline where you want to build and upload an image, add a Plugin step that uses the buildah plugin.

Name: Enter a name.
Container Registry: Select a connector corresponding to your push destination.
- Docker Hub: Docker connector
- ACR: Azure connector
- ECR: AWS connector
- GAR/GCR: GCP connector
Image: Specify the plugin image and tag to use, such as plugins/buildah-docker:1.1.0-linux-amd64. If you don't specify a tag, the latest tag is used by default. Go to an image's Docker Hub page to browse available tags:
- ACR: buildah-acr
- ECR: buildah-ecr
- GAR/GCR: buildah-gcr
- Docker Hub: buildah-docker
Privileged: Set to false for OpenShift clusters; true for standard Kubernetes.
Run as User: Specify the ID of the non-root user to use for this step, such as 1000.
Settings: Add the following settings as key-value pairs.
- repo: The name of the repository where you want to store the image, for example, <hub-user>/<repo-name>. For private registries, specify a fully qualified repo name.
- tags: Specify tags for your image.
- registry: Specify the registry index, such as https://index.docker.io/v2/. The registry format for ECR is aws_account_id.dkr.ecr.region.amazonaws.com.
- dockerfile: Specify the Dockerfile to use for the build.
- username: Provide the username to access the push destination, either as plaintext or an expression referencing a Harness secret or pipeline variable, such as <+pipeline.variables.DOCKER_HUB_USER>.
- password: An expression referencing a Harness secret or pipeline variable containing the password to access the push destination, such as <+pipeline.variables.DOCKER_HUB_SECRET>.
- For more information and additional settings, including AWS S3 settings, go to Buildah plugin settings.

At the point in your pipeline where you want to build and upload an image, add a Plugin step that uses the buildah plugin, for example:

                - step:
                    type: Plugin
                    name: buildah-docker
                    identifier: buildahdocker
                    spec:
                      connectorRef: YOUR_DOCKER_CONNECTOR
                      image: plugins/buildah-docker:1.1.0-linux-amd64
                      privileged: true     # false for OpenShift with anyuid SCC
                      settings:
                        repo: myDockerHub1234/test
                        tags: buildahtest
                        registry: https://index.docker.io/v2/
                        dockerfile: Dockerfile
                        username: <+secrets.getValue("DOCKER_HUB_USER")>
                        password: <+secrets.getValue("DOCKER_HUB_SECRET")>
                      runAsUser: "1000"

This step requires the following specifications:

connectorRef: Provide the ID of a Docker connector.
image: Specify the plugin image and tag to use, such as plugins/buildah-docker:1.1.0-linux-amd64. If you don't specify a tag, the latest tag is used by default. Go to an image's Docker Hub page to browse available tags:
- ACR: buildah-acr
- ECR: buildah-ecr
- GAR/GCR: buildah-gcr
- Docker Hub: buildah-docker
privileged: Set to false for OpenShift clusters. Set to true for non-OpenShift clusters.
runAsUser: Specify the ID of the non-root user to use for this step, such as 1000.
settings: Add the following settings as key-value pairs.
- repo: The name of the repository where you want to store the image, for example, <hub-user>/<repo-name>. For private registries, specify a fully qualified repo name.
- tags: Specify tags for your image.
- registry: Specify the registry index, such as https://index.docker.io/v2/. The registry format for ECR is aws_account_id.dkr.ecr.region.amazonaws.com.
- dockerfile: Specify the Dockerfile to use for the build.
- username: Provide the username to access the push destination, either as plaintext or an expression referencing a Harness secret or pipeline variable, such as <+pipeline.variables.DOCKER_HUB_USER>.
- password: An expression referencing a Harness secret or pipeline variable containing the password to access the push destination, such as <+pipeline.variables.DOCKER_HUB_SECRET>.
- For more information and additional settings, including AWS S3 settings, go to Buildah plugin settings.

Buildah plugin settings

For information about Buildah plugin settings, go to the Buildah README, the Buildah Drone Plugins Marketplace page, and the main.go file for each destination:

Many Buildah plugin settings correspond with settings for the built-in Build and Push steps. If you're encountering an error with the buildah plugin configuration, you can reference the settings definitions for the built-in steps for guidance on the expected value for the equivalent Buildah settings. However, keep in mind that the configuration for Build and Push steps (such as field names and location in the YAML) is not an exact match to the Plugin step configuration.

Destination

Buildah image

Buildah main.go

Equivalent Build and Push step

Docker Hub

buildah-docker

Docker main.go

Build and Push to Docker Registry

ACR

buildah-acr

ACR main.go

Build and Push to ACR

ECR

buildah-ecr

ECR main.go

Build and Push to ECR

GAR

buildah-grc

GCR main.go

Build and Push to GAR

Stage YAML example

This YAML example shows a Build (CI) stage with a Kubernetes cluster build infrastructure running as non-root (runAsNonRoot: true and runAsUser: "1000") and a Plugin step running the Buildah plugin.

    - stage:
        identifier: stage1
        type: CI
        name: stage1
        spec:
          cloneCodebase: true
          infrastructure:
            type: KubernetesDirect
            spec:
              connectorRef: YOUR_KUBERNETES_CLUSTER_CONNECTOR
              namespace: YOUR_NAMESPACE
              automountServiceAccountToken: true
              nodeSelector: {}
              containerSecurityContext:
                runAsNonRoot: true
                runAsUser: "1000"
              os: Linux
          execution:
            steps:
              - step:
                  identifier: buildah plugin
                  type: Plugin
                  name: buildah_plugin
                  spec:
                    connectorRef: YOUR_DOCKER_CONNECTOR
                    image: plugins/buildah-docker:1.1.0-linux-amd64
                    privileged: true
                    settings:
                      repo: myhub/test-repo
                      tags: builadhrootless
                      registry: https://index.docker.io/v2/
                      dockerfile: Dockerfile2
                      username: <+pipeline.variables.DOCKER_HUB_USER>
                      password: <+secrets.getValue("MyDockerPAT")>
                    runAsUser: "1000"

Build an image without pushing

You can use your CI pipeline to test a Dockerfile used in your codebase and verify that the resulting image is correct before you push it to your Docker repository.

The following configuration is valid with the Docker Buildah plugin (plugins/buildah-docker) only. For other configurations, go to Build without pushing.

In your CI pipeline, go to the Build stage that includes the Plugin step with the Docker Buildah plugin.
In the Build stage's Overview tab, expand the Advanced section.
Select Add Variable and enter the following:
- Name: PLUGIN_DRY_RUN
- Type: String
- Value: true
Save and run the pipeline.

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