Prerequisite

All examples in this guide use the public image. If you've mirrored the repository for your own use (for example, to your Docker Hub namespace), update your commands to reference the mirrored image instead of the public one.

For example:

• Public image: dhi.io/<repository>:<tag>
• Mirrored image: <your-namespace>/dhi-<repository>:<tag> For the examples, you must first use docker login dhi.io to authenticate to the registry to pull the images.

Start a Fluent Bit instance

Run the following command to start a Fluent Bit container. The image's entrypoint is the fluent-bit binary, and a reference configuration is bundled read-only at /fluent-bit/etc/conf/fluent-bit.conf inside the image. Unlike some Fluent Bit distributions, the hardened image does not auto-load a configuration file at startup — you must pass a config explicitly with the -c flag when you need inputs, filters, or outputs. To use your own configuration, replace <path-to-your-configuration-file> with the path to your fluent-bit.conf file.

# Start with the bundled reference config
$ docker run --rm --name my-fluentbit -p 24224:24224 \
  dhi.io/fluent-bit:<tag> \
  -c /fluent-bit/etc/conf/fluent-bit.conf

# Start with a custom config
$ docker run --rm --name my-fluentbit -p 24224:24224 \
  -v <path-to-your-configuration-file>:/fluent-bit/etc/conf/fluent-bit.conf:ro \
  dhi.io/fluent-bit:<tag> \
  -c /fluent-bit/etc/conf/fluent-bit.conf

The image exposes 24224/tcp (Forward input), 9880/tcp (HTTP input), and 2020/tcp (built-in HTTP server for health and metrics). Publish any ports your configuration uses with -p. Note that port 2020 only listens when http_server On is set in the [SERVICE] block of your config — the port is exposed in image metadata but nothing binds to it by default.

Common Fluent Bit use cases

Basic log forwarding with HTTP input

Create a configuration that accepts JSON payloads on port 9880 and prints them to stdout:

Create fluent-bit.conf:

[SERVICE]
    flush        1
    log_level    info
    http_server  On
    http_listen  0.0.0.0
    http_port    2020

[INPUT]
    name http
    host 0.0.0.0
    port 9880

[OUTPUT]
    name  stdout
    match *

Run Fluent Bit with the configuration:

$ docker run -d --name fluent-bit -p 9880:9880 -p 2020:2020 \
  -v $(pwd)/fluent-bit.conf:/fluent-bit/etc/conf/fluent-bit.conf:ro \
  dhi.io/fluent-bit:<tag> \
  -c /fluent-bit/etc/conf/fluent-bit.conf

Send a JSON log entry and verify it appears in the container logs:

$ curl -X POST -H 'Content-Type: application/json' \
    -d '{"message":"hello world"}' \
    http://localhost:9880/test.log

$ docker logs fluent-bit | tail -2
[0] test.log: [[1776688797.501994961, {}], {"message"=>"hello world"}]

Verify the built-in HTTP server is running:

$ curl http://localhost:2020/
{"fluent-bit":{"version":"5.4","edition":"Community", ... }}

Deploy to Kubernetes with the DHI Helm chart

For Kubernetes deployments, use the Docker Hardened Helm chart at oci://dhi.io/fluent-bit-chart. The chart pins all container images (Fluent Bit, configmap-reload, and the test BusyBox) by SHA256 digest, so you get supply-chain integrity without extra configuration.

Step 1: Create an image pull secret. The DHI registry requires authentication for cluster pulls. Create a Kubernetes secret using your Docker Hub credentials:

$ kubectl create secret docker-registry helm-pull-secret \
    --docker-server=dhi.io \
    --docker-username=<Docker username> \
    --docker-password=<Docker token> \
    --docker-email=<Docker email>

Use a Docker Hub personal access token (not your account password). For more detail, see the DHI Kubernetes authentication guide⁠.

Step 2: Install the chart. Replace <tag> with a published chart version (for example, 0.57.3):

$ helm install my-fluent-bit oci://dhi.io/fluent-bit-chart --version <tag> \
    --set "imagePullSecrets[0].name=helm-pull-secret"

The chart deploys a DaemonSet that tails container logs on each node, enriches records with Kubernetes pod metadata via the Kubernetes API, and forwards them to configured outputs.

Step 3: Verify the deployment.

$ kubectl get daemonset,pod -l app.kubernetes.io/instance=my-fluent-bit
NAME                                            DESIRED   CURRENT   READY   AGE
daemonset.apps/my-fluent-bit-fluent-bit-chart   2         2         2       15s

NAME                                       READY   STATUS    RESTARTS   AGE
pod/my-fluent-bit-fluent-bit-chart-bcz69   1/1     Running   0          15s
pod/my-fluent-bit-fluent-bit-chart-zn7td   1/1     Running   0          15s

Confirm the running pods are the digest-pinned DHI image:

$ kubectl get pod -l app.kubernetes.io/instance=my-fluent-bit \
    -o jsonpath='{.items[0].spec.containers[0].image}'
dhi.io/fluent-bit:5.4-debian13@sha256:817c1d8898b31ab5b06dd393ae8ebf92f0230da3cbf4a2673d8fee45b93b32de

Port-forward to a pod and hit the Fluent Bit HTTP server:

$ export POD_NAME=$(kubectl get pods -l app.kubernetes.io/instance=my-fluent-bit \
    -o jsonpath="{.items[0].metadata.name}")
$ kubectl port-forward $POD_NAME 2020:2020
$ curl http://127.0.0.1:2020/

To customize outputs, parsers, or filters, override the config values when installing the chart. See the chart's values schema: helm show values oci://dhi.io/fluent-bit-chart --version <tag>.

To uninstall:

$ helm -n default uninstall my-fluent-bit

Inspect health and metrics

Fluent Bit exposes a built-in HTTP server when http_server On is set. It provides operational endpoints useful for liveness probes, Prometheus scraping, and runtime inspection:

$ curl http://localhost:2020/               # build info and compiled features
$ curl http://localhost:2020/api/v1/health  # liveness
$ curl http://localhost:2020/api/v1/uptime  # uptime
$ curl http://localhost:2020/api/v1/metrics/prometheus  # Prometheus metrics

Non-hardened images vs Docker Hardened Images

Key differences

Why no shell or package manager?

Docker Hardened Images prioritize security through minimalism:

• Reduced attack surface: Fewer binaries mean fewer potential vulnerabilities

• Immutable infrastructure: Runtime containers shouldn't be modified after deployment

• Compliance ready: Meets strict security requirements for regulated environments The Fluent Bit hardened image includes bash and GNU coreutils for config templating and entrypoint scripting, but deliberately omits package managers, network utilities (curl, wget), editors, and process inspection tools (ps, top, find). Common debugging methods for applications built with Docker Hardened Images include:

• Docker Debug⁠ to attach to containers

• Docker's Image Mount feature to mount debugging tools

• Fluent Bit's built-in HTTP server on port 2020 for health, uptime, and metrics Docker Debug provides a shell, common debugging tools, and lets you install other tools in an ephemeral, writable layer that only exists during the debugging session. For example:

$ docker debug fluent-bit

Or mount debugging tools with the Image Mount feature:

$ docker run --rm -it --pid container:fluent-bit \
  --mount=type=image,source=dhi.io/busybox:1,destination=/dbg,ro \
  --entrypoint /dbg/bin/sh \
  dhi.io/fluent-bit:<tag>

Image variants

Docker Hardened Images come in different variants depending on their intended use.

Runtime variants are designed to run your application in production. These images are intended to be used either directly or as the FROM image in the final stage of a multi-stage build. These images typically:

• Run as the nonroot user (UID 65532)

• Do not include a package manager

• Contain only the minimal set of libraries needed to run the app Build-time variants include dev in the variant name and are intended for use in the first stage of a multi-stage Dockerfile. These images typically:

• Run as the root user

• Include a shell and package manager

• Are used to build or compile applications, or to install additional Fluent Bit plugins and dependencies To view all published tags and get more information about each variant, select the Tags tab for this repository.

FIPS variants

FIPS variants include fips in the variant name and tag. They come in both runtime and build-time variants. These variants use cryptographic modules that have been validated under FIPS 140, a U.S. government standard for secure cryptographic operations.

The Fluent Bit FIPS variants are available through DHI Select and DHI Enterprise subscriptions only. To pull them, mirror the repository into your own namespace and pull from your mirror. See Mirror a DHI repository⁠.

FIPS variants of the Fluent Bit image carry the compliance labels fips,stig,cis and are drop-in replacements for the standard runtime variant — same entrypoint, same nonroot UID 65532. No changes are required to the Fluent Bit binary or config file to run under FIPS mode.

Verify the FIPS attestation

FIPS variants include a signed FIPS attestation listing the cryptographic modules in the image and their validation status. Retrieve it with Docker Scout against your mirrored repository:

$ docker scout attest get \
    --predicate-type https://docker.com/dhi/fips/v0.1 \
    --predicate \
    <your-namespace>/dhi-fluent-bit:<tag>-fips

Runtime requirements specific to FIPS

Fluent Bit itself does not require any FIPS-specific configuration flags. TLS operations for outputs (Elasticsearch, HTTP, Forward, Kafka, etc.) automatically use the FIPS-validated cryptographic providers.

If you use outputs that depend on non-approved cryptographic algorithms (for example, legacy TLS 1.0/1.1 endpoints or certificates signed with MD5), those will fail at runtime rather than silently falling back. Review your tls.* settings and certificate chain for FIPS compatibility before deploying a FIPS variant.

What changes in FIPS mode

Compared to the standard runtime variant:

• Cryptographic modules: OpenSSL FIPS Provider is used for all cryptographic operations
• Available algorithms: only FIPS 140-approved algorithms are available
• Image size: slightly larger due to the FIPS provider module
• Compliance labels: carries com.docker.dhi.compliance=fips,stig,cis
• Everything else: identical. Same Fluent Bit version, same CLI, same config format, same nonroot UID 65532 FIPS variants are appropriate for regulated environments such as FedRAMP, government, healthcare, financial services, and defense deployments.

Migrate to a Docker Hardened Image

To migrate your Fluent Bit deployment to a Docker Hardened Image, you must update your Dockerfile or Compose file. At minimum, update the base image. The following table lists the most common changes:

The following steps outline the general migration process.

1. Find hardened images for your app. A hardened image may have several variants. Inspect the image tags and find the image variant that meets your needs.
2. Update the base image in your Dockerfile. Update the base image in your application's Dockerfile to the hardened image you found in the previous step. For plugin installation, use an image tagged as dev because it has the tools needed to install packages and dependencies.
3. For multi-stage Dockerfiles, update the runtime image in your Dockerfile. To ensure that your final image is as minimal as possible, you should use a multi-stage build. All stages in your Dockerfile should use a hardened image. While intermediary stages will typically use images tagged as dev, your final runtime stage should use a runtime variant.
4. Install additional packages. Docker Hardened Images contain minimal packages in order to reduce the potential attack surface. For Fluent Bit plugins, install them in the build stage using a dev image and copy the necessary artifacts to the runtime stage.

Troubleshoot migration

General debugging

The hardened image includes bash and GNU coreutils but no networking or package-management tools. Most operational debugging can be done through Fluent Bit's built-in HTTP server on port 2020 (see Inspect health and metrics⁠ for the available endpoints).

For deeper inspection, use Docker Debug⁠ to attach to a running container with a full debugging toolchain.

Permissions

By default runtime variants run as the nonroot user (UID 65532). Ensure that necessary files and directories are accessible to this UID:

COPY --chown=65532:65532 fluent-bit.conf /fluent-bit/etc/conf/fluent-bit.conf

Fluent Bit's position database (DB setting on the tail input), filesystem storage path (storage.path), and any host volumes it writes to must all be writable by UID 65532. Docker auto-creates named volumes as root:root, which the nonroot user cannot write to — either pre-chown the volume or use a fsGroup: 65532securityContext in Kubernetes.

Privileged ports

Runtime variants run as a nonroot user by default. Applications in these images can't bind to privileged ports (below 1024) when running in Kubernetes or in Docker Engine versions older than 20.10. Fluent Bit's default ports (9880, 24224, and 2020) are all above 1024 and are unaffected. If you configure custom input sources, ensure they also use ports above 1024.

No shell

Runtime variants include bash but omit package managers, editors, and networking tools. For build-time tasks (installing plugins, compiling custom outputs, templating configs) use the dev variant. For runtime debugging beyond Fluent Bit's HTTP API, use Docker Debug.

Entry point

Docker Hardened Images may have different entry points than images such as Docker Official Images. Use docker inspect to inspect entry points for Docker Hardened Images and update your Dockerfile if necessary.