Complete Guide to Managing CA Certificates in Podman

Table of Contents#

Overview#

Managing Certificate Authority (CA) certificates in Podman is crucial for working with private registries, internal services, and corporate networks. This guide provides detailed methods for adding CA certificates to Podman and integrating with custom PKI infrastructure.

Architecture Overview#

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graph TB
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    subgraph "Certificate Sources"
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        A[Corporate CA]
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        B[Smallstep CA]
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        C[Internal PKI]
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    end
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    subgraph "Podman Machine"
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        D[/etc/pki/ca-trust/source/anchors]
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        E[update-ca-trust]
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        F[System Trust Store]
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    end
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    subgraph "Container Runtime"
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        G[Podman Engine]
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        H[Container Registries]
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        I[Container Services]
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    end
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    A --> D
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    B --> D
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    C --> D
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    D --> E
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    E --> F
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    F --> G
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    G --> H
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    G --> I
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    style D fill:#ffd43b,stroke:#fab005,stroke-width:2px
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    style F fill:#74c0fc,stroke:#1971c2,stroke-width:2px
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    style G fill:#4ecdc4,stroke:#087f5b,stroke-width:2px

Installation Methods#

Method 1: Downloading Certificates#

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# 1. SSH into Podman machine
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podman machine ssh
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# 2. Switch to root user (if needed)
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sudo su -
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# 3. Navigate to certificate directory
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cd /etc/pki/ca-trust/source/anchors
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# 4. Download certificate from server
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curl -k -o custom-ca.crt https://ca-server.example.com/ca.crt
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# 5. Update system trust store
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update-ca-trust

Method 2: Manual Certificate Creation#

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# 1. Connect to Podman machine
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podman machine ssh
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# 2. Switch to root
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sudo su -
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# 3. Navigate to certificate directory
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cd /etc/pki/ca-trust/source/anchors
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# 4. Create certificate file
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vi custom-ca.crt
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# 5. Paste certificate content (including BEGIN/END lines)
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# -----BEGIN CERTIFICATE-----
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# [Certificate content]
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# -----END CERTIFICATE-----
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# 6. Update trust store
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update-ca-trust

Integration with Custom PKI#

Complete Infrastructure Setup#

1
sequenceDiagram
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    participant CA as Smallstep CA
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    participant DNS as CoreDNS
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    participant PM as Podman Machine
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    participant CR as Container Registry
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    participant C as Containers
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    CA->>CA: Generate Root CA
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    CA->>PM: Install Root Certificate
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    PM->>PM: update-ca-trust
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    DNS->>C: Resolve internal domains
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    C->>CR: Pull images (HTTPS)
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    CR->>CA: Validate certificate
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    CA->>CR: Certificate valid
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    CR->>C: Image delivered

Setting Up Smallstep CA Integration#

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# 1. SSH into Podman machine
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podman machine ssh
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# 2. Switch to root
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sudo su -
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# 3. Navigate to certificate directory
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cd /etc/pki/ca-trust/source/anchors
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# 4. Get certificate from Smallstep CA
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curl -k -o invinsense-ca.pem https://ca.invinsense/root_ca.crt
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# 5. Update trust store
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update-ca-trust
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# 6. Exit
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exit
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exit

Advanced Configuration#

Container Registry Trust#

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graph LR
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    subgraph "Podman Configuration"
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        A[registries.conf]
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        B[Trust Settings]
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        C[DNS Resolution]
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    end
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    subgraph "Registry Communication"
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        D[Internal Registry]
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        E[External Registry]
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        F[Mirror Registry]
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    end
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    A --> D
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    B --> D
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    C --> D
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    A --> E
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    A --> F
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    style A fill:#ffd43b,stroke:#fab005,stroke-width:2px
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    style B fill:#ff6b6b,stroke:#c92a2a,stroke-width:2px
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    style D fill:#4ecdc4,stroke:#087f5b,stroke-width:2px

Registry Configuration#

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# Configure Podman for internal registries
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podman machine ssh
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sudo vi /etc/containers/registries.conf

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# Add to registries.conf
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[registries.search]
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registries = ['docker.io', 'registry.invinsense']
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[registries.insecure]
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registries = []
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[registries.block]
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registries = []
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# For specific registry with custom CA
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[[registry]]
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prefix = "registry.invinsense"
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location = "registry.invinsense"

Automated Certificate Management#

Automation Script#

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#!/bin/bash
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# setup-podman-ca.sh - Automated CA certificate installation
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set -e
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# Configuration
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CA_URL="${CA_URL:-https://ca.invinsense/root_ca.crt}"
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CA_NAME="${CA_NAME:-custom-ca.crt}"
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PODMAN_MACHINE="${PODMAN_MACHINE:-podman-machine-default}"
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# Function to install CA certificate
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install_ca_cert() {
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    echo "Installing CA certificate..."
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    # Create temporary script
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    cat << 'EOF' > /tmp/install-ca.sh
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#!/bin/bash
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cd /etc/pki/ca-trust/source/anchors
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curl -k -o ${CA_NAME} ${CA_URL}
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update-ca-trust
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echo "CA certificate installed successfully"
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EOF
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    # Copy and execute script in Podman machine
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    podman machine ssh ${PODMAN_MACHINE} < /tmp/install-ca.sh
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    # Cleanup
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    rm -f /tmp/install-ca.sh
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}
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# Main execution
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echo "Setting up CA certificates for Podman..."
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install_ca_cert
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echo "Testing certificate trust..."
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podman machine ssh ${PODMAN_MACHINE} "curl -s https://ca.invinsense"
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echo "Setup complete!"

Comparison: Smallstep CA vs Manual Setup#

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graph TD
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    A[Certificate Management] --> B[Smallstep CA]
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    A --> C[Manual CA]
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    B --> D[Automated Lifecycle]
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    B --> E[API Integration]
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    B --> F[Audit Trails]
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    B --> G[Easy Renewal]
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    C --> H[Simple Setup]
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    C --> I[Direct Control]
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    C --> J[No Infrastructure]
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    C --> K[Manual Renewal]
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    style B fill:#4ecdc4,stroke:#087f5b,stroke-width:2px
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    style C fill:#ffd43b,stroke:#fab005,stroke-width:2px
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    style D fill:#d0f0c0,stroke:#5cb85c,stroke-width:2px
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    style K fill:#ff6b6b,stroke:#c92a2a,stroke-width:2px

Smallstep CA Advantages#

Centralized Management

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# Automated certificate issuance
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step ca certificate service.invinsense cert.pem key.pem

Automated Renewal

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# Set up automatic renewal
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step ca renew --daemon cert.pem key.pem

Revocation Support

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# Revoke compromised certificates
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step ca revoke --serial $SERIAL_NUMBER

Security Best Practices#

Certificate Validation Workflow#

1
sequenceDiagram
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    participant PM as Podman Machine
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    participant TS as Trust Store
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    participant PE as Podman Engine
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    participant R as Registry
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    PM->>TS: Add CA certificate
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    TS->>TS: Validate certificate
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    PE->>R: Connect to registry
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    R->>PE: Present certificate
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    PE->>TS: Verify certificate chain
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    TS->>PE: Certificate trusted
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    PE->>R: Establish secure connection

Security Checklist#

Verify certificate authenticity before installation
Use secure channels for certificate distribution
Regularly rotate certificates
Monitor certificate expiration
Implement proper access controls
Maintain certificate backups

Troubleshooting#

Common Issues and Solutions#

1. Certificate Not Trusted#

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# Verify certificate installation
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ls -la /etc/pki/ca-trust/source/anchors/
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# Check certificate format
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openssl x509 -in /etc/pki/ca-trust/source/anchors/custom-ca.crt -text -noout
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# Force trust store update
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update-ca-trust force-enable
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update-ca-trust extract

2. Registry Connection Failures#

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# Test registry connection
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podman pull registry.example.com/test:latest
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# Debug with verbose output
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podman --log-level=debug pull registry.example.com/test:latest
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# Check DNS resolution
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nslookup registry.example.com

3. Certificate Chain Issues#

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graph TD
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    A[Certificate Chain Issue] --> B{Diagnosis}
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    B --> C[Missing Intermediate]
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    B --> D[Wrong Order]
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    B --> E[Expired Certificate]
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    C --> F[Add intermediate CA]
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    D --> G[Reorder certificates]
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    E --> H[Renew certificate]
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    style A fill:#ff6b6b,stroke:#c92a2a,stroke-width:2px
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    style B fill:#ffd43b,stroke:#fab005,stroke-width:2px

Container-Specific Trust#

Injecting Certificates into Containers#

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# Dockerfile example
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FROM alpine:latest
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# Copy CA certificate
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COPY ca-certificates/ /usr/local/share/ca-certificates/
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# Update CA certificates
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RUN update-ca-certificates
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# Your application
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COPY app /app
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CMD ["/app"]

Runtime Certificate Injection#

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# Mount host CA certificates into container
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podman run -v /etc/pki/ca-trust:/etc/pki/ca-trust:ro \
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  -v /etc/ssl/certs:/etc/ssl/certs:ro \
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  myapp:latest

Integration with CI/CD#

GitLab CI Example#

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stages:
2
  - setup
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  - build
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  - deploy
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setup-ca:
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  stage: setup
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  script:
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    - |
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      podman machine ssh << EOF
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      sudo curl -k -o /etc/pki/ca-trust/source/anchors/company-ca.crt \
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        ${CA_SERVER_URL}/ca.crt
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      sudo update-ca-trust
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      EOF
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build:
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  stage: build
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  needs: [setup-ca]
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  script:
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    - podman build -t ${CI_REGISTRY_IMAGE}:${CI_COMMIT_SHA} .
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    - podman push ${CI_REGISTRY_IMAGE}:${CI_COMMIT_SHA}

Certificate Lifecycle Management#

1
stateDiagram-v2
2
    [*] --> Generate
3
    Generate --> Distribute
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    Distribute --> Install
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    Install --> Monitor
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    Monitor --> Renew: Near expiration
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    Monitor --> Revoke: Compromised
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    Renew --> Distribute
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    Revoke --> Generate: New certificate needed
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    Monitor --> [*]: Certificate expired

Best Practices Summary#

Use Centralized CA Management
- Implement Smallstep CA or similar solution
- Automate certificate distribution
- Enable automatic renewal
Secure Certificate Handling
- Never expose private keys
- Use encrypted channels for distribution
- Implement proper access controls
Monitor and Maintain
- Set up expiration alerts
- Regular security audits
- Document certificate locations
Container Integration
- Build certificates into base images
- Use volume mounts for dynamic updates
- Implement certificate rotation strategies

Conclusion#

Proper CA certificate management in Podman is essential for secure container operations in enterprise environments. Whether using manual installation or automated solutions like Smallstep CA, following these practices ensures reliable and secure container communications.

Key takeaways:

Multiple methods exist for CA certificate installation
Automated solutions provide better lifecycle management
Proper trust configuration enables secure registry access
Regular monitoring and maintenance are essential
Integration with existing PKI infrastructure streamlines operations

By implementing these strategies, you can ensure your Podman environments maintain proper certificate trust while supporting your organization’s security requirements.