x.509 certificate exporter

Common x509-certificate-exporter Hardened Image use cases

This guide provides practical examples for using the x509-certificate-exporter Hardened Image to monitor X.509 certificate expiration in Kubernetes clusters or standalone environments.

Source configuration is required in v4

Version 4 requires at least one source to be configured at startup. If you start the container without a config file or without one of the source flags such as --watch-dir, --watch-file, --watch-kubeconf, or --watch-kube-secrets, the exporter exits with fatal: no sources configured.

All examples below include a source configuration for that reason.

Run a x509-certificate-exporter container

Basic usage with certificate directory

docker run -d --name x509-exporter \
    -p 9793:9793 \
    -v /path/to/certs:/certs:ro \
    registry.ghost-prod.alphabravo.io/ghost-base/x509-certificate-exporter:<tag> \
    --watch-dir=/certs

With custom listen address

docker run -d --name x509-exporter \
    -p 8080:8080 \
    -v /path/to/certs:/certs:ro \
    registry.ghost-prod.alphabravo.io/ghost-base/x509-certificate-exporter:<tag> \
    --watch-dir=/certs \
    --listen-address=:8080

Run with Docker Compose

Monitor a single certificate directory

1. Create Docker Compose:

Create docker-compose.yaml.

services:
  x509-exporter:
    image: registry.ghost-prod.alphabravo.io/ghost-base/x509-certificate-exporter:<tag>
    ports:
      - "9793:9793"
    volumes:
      - /etc/ssl/certs:/certs:ro
    command:
      - --watch-dir=/certs
    restart: unless-stopped

1. Start the exporter:

docker compose up -d

1. Verify it's running:

curl http://localhost:9793/metrics | grep x509_cert

Monitor multiple certificate directories

Use docker-compose.yaml:

services:
  x509-exporter:
    image: registry.ghost-prod.alphabravo.io/ghost-base/x509-certificate-exporter:<tag>
  ports:
    - "9793:9793"
  volumes:
    - /etc/ssl/certs:/certs:ro
    - /etc/pki/tls:/tls:ro
    - /app/certificates:/app-certs:ro
  command:
    - --watch-dir=/certs
    - --watch-dir=/tls
    - --watch-dir=/app-certs
  restart: unless-stopped

Integration with Prometheus

1. Create docker-compose.yaml with Prometheus:

services:
  x509-exporter:
    image: registry.ghost-prod.alphabravo.io/ghost-base/x509-certificate-exporter:<tag>
    ports:
      - "9793:9793"
    volumes:
      - /etc/ssl/certs:/certs:ro
    command:
      - --watch-dir=/certs
restart: unless-stopped

  prometheus:
    image: prom/prometheus:latest
    ports:
      - "9090:9090"
    volumes:
      - ./prometheus.yml:/etc/prometheus/prometheus.yml:ro
    command:
      - --config.file=/etc/prometheus/prometheus.yml
    depends_on:
      - x509-exporter

1. Create prometheus.yml

global:
  scrape_interval: 60s

scrape_configs:
  - job_name: 'x509-exporter'
    static_configs:
      - targets: ['x509-exporter:9793']

1. Start the stack:

docker compose up -d

1. Access Prometheus at http://localhost:9090 and query certificate metrics:

# Certificates expiring in less than 30 days
x509_cert_not_after - time() < 86400 * 30

# Expired certificates
x509_cert_expired == 1

Use x509-certificate-exporter in Kubernetes

1. Deploy as a DaemonSet to monitor certificates on all nodes:

apiVersion: apps/v1
kind: DaemonSet
metadata:
  name: x509-certificate-exporter
  namespace: monitoring
spec:
  selector:
    matchLabels:
      app: x509-certificate-exporter
  template:
    metadata:
      labels:
        app: x509-certificate-exporter
    spec:
      containers:
        - name: x509-exporter
          image: registry.ghost-prod.alphabravo.io/ghost-base/x509-certificate-exporter:<tag>
          args:
            - --watch-dir=/host-certs
            - --watch-dir=/host-pki
          ports:
            - containerPort: 9793
              name: metrics
          volumeMounts:
            - name: host-certs
              mountPath: /host-certs
              readOnly: true
            - name: host-pki
              mountPath: /host-pki
              readOnly: true
          livenessProbe:
            httpGet:
              path: /healthz
              port: 9793
            initialDelaySeconds: 10
            periodSeconds: 30
          readinessProbe:
            httpGet:
              path: /healthz
              port: 9793
            initialDelaySeconds: 5
            periodSeconds: 10
      volumes:
        - name: host-certs
          hostPath:
            path: /etc/ssl/certs
        - name: host-pki
          hostPath:
            path: /etc/pki/tls
      imagePullSecrets:
        - name: <your-registry-secret>
---
apiVersion: v1
kind: Service
metadata:
  name: x509-certificate-exporter
  namespace: monitoring
  labels:
    app: x509-certificate-exporter
spec:
  ports:
    - port: 9793
      targetPort: 9793
      name: metrics
  selector:
    app: x509-certificate-exporter

1. Apply the manifest:

kubectl apply -f x509-exporter.yaml

1. Verify the deployment:

kubectl get pods -n monitoring -l app=x509-certificate-exporter

Monitor Kubernetes secrets

1. Deploy as a Deployment to watch Kubernetes TLS secrets:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: x509-certificate-exporter
  namespace: monitoring
spec:
  replicas: 1
  selector:
    matchLabels:
      app: x509-certificate-exporter
  template:
    metadata:
      labels:
        app: x509-certificate-exporter
    spec:
      serviceAccountName: x509-certificate-exporter
      containers:
        - name: x509-exporter
          image: registry.ghost-prod.alphabravo.io/ghost-base/x509-certificate-exporter:<tag>
          args:
            - --watch-kube-secrets
          ports:
            - containerPort: 9793
              name: metrics
          livenessProbe:
            httpGet:
              path: /healthz
              port: 9793
            initialDelaySeconds: 10
            periodSeconds: 30
          readinessProbe:
            httpGet:
              path: /healthz
              port: 9793
            initialDelaySeconds: 5
            periodSeconds: 10
      imagePullSecrets:
        - name: <your-registry-secret>
---
apiVersion: v1
kind: ServiceAccount
metadata:
  name: x509-certificate-exporter
  namespace: monitoring
---
apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRole
metadata:
  name: x509-certificate-exporter
rules:
  - apiGroups: [""]
    resources: ["secrets"]
    verbs: ["get", "list", "watch"]
---
apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRoleBinding
metadata:
  name: x509-certificate-exporter
roleRef:
  apiGroup: rbac.authorization.k8s.io
  kind: ClusterRole
  name: x509-certificate-exporter
subjects:
  - kind: ServiceAccount
    name: x509-certificate-exporter
    namespace: monitoring

Prometheus ServiceMonitor (for Prometheus Operator)

apiVersion: monitoring.coreos.com/v1
kind: ServiceMonitor
metadata:
  name: x509-certificate-exporter
  namespace: monitoring
spec:
  selector:
    matchLabels:
      app: x509-certificate-exporter
  endpoints:
    - port: metrics
      interval: 60s
      path: /metrics

Common metrics

The exporter exposes Prometheus metrics for both certificate state and exporter health. Common metrics include:

Command-line options

Common command-line flags:

Non-hardened images vs Ghost hardened images

Key differences

Why no shell or package manager?

Ghost 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

Hardened image debugging

The hardened images intended for runtime don't contain a shell nor any tools for debugging. Common debugging methods for applications built with Ghost hardened images include:

• Docker Debug to attach to containers
• Docker's Image Mount feature to mount debugging tools
• Ecosystem-specific debugging approaches

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, you can use Docker Debug:

docker debug registry.ghost-prod.alphabravo.io/ghost-base/x509-certificate-exporter:<tag>

or mount debugging tools with the Image Mount feature:

docker run --rm -it --pid container:my-container \
  --mount=type=image,source=registry.ghost-prod.alphabravo.io/ghost-base/busybox,destination=/dbg,ro \
  registry.ghost-prod.alphabravo.io/ghost-base/x509-certificate-exporter:<tag> /dbg/bin/sh

Image variants

Ghost 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
  • Do not include a shell or a package manager
  • Contain only the minimal set of libraries needed to run the app

• Build-time variants typically 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

• FIPS variants include fips in the variant name and tag. These variants use cryptographic modules that have been validated under FIPS 140, a U.S. government standard for secure cryptographic operations. For example, usage of MD5 fails in FIPS variants.

Migrate to a Ghost hardened image

To migrate your application to a Ghost hardened image, you must update your Dockerfile. At minimum, you must update the base image in your existing Dockerfile to a Ghost hardened image. This and a few other common changes are listed in the following table of migration notes.

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 framework images, this is typically going to be 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 non-dev image variant.

4. Install additional packages

   Ghost hardened images contain minimal packages in order to reduce the potential attack surface. You may need to install additional packages in your Dockerfile. Inspect the image variants to identify which packages are already installed.

   Only images tagged as dev typically have package managers. You should use a multi-stage Dockerfile to install the packages. Install the packages in the build stage that uses a dev image. Then, if needed, copy any necessary artifacts to the runtime stage that uses a non-dev image.

   For Alpine-based images, you can use apk to install packages. For Debian-based images, you can use apt-get to install packages.

Troubleshooting migration

The following are common issues that you may encounter during migration.

General debugging

The hardened images intended for runtime don't contain a shell nor any tools for debugging. The recommended method for debugging applications built with Ghost hardened images is to use Docker Debug to attach to these containers. 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.

Permissions

By default image variants intended for runtime, run as the nonroot user. Ensure that necessary files and directories are accessible to the nonroot user. You may need to copy files to different directories or change permissions so your application running as the nonroot user can access them.

Privileged ports

Non-dev hardened images run as a nonroot user by default. As a result, 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. To avoid issues, configure your application to listen on port 1025 or higher inside the container, even if you map it to a lower port on the host. For example, docker run -p 80:8080 my-image will work because the port inside the container is 8080, and docker run -p 80:81 my-image won't work because the port inside the container is 81.

No shell

By default, image variants intended for runtime don't contain a shell. Use dev images in build stages to run shell commands and then copy any necessary artifacts into the runtime stage. In addition, use Docker Debug to debug containers with no shell.

Entry point

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