Local Secrets

Pipeline configurations often require credentials for databases, APIs, and message queues. Local secrets use environment variables and files to provide these credentials without hard-coding values in YAML.

Assumption

This guide assumes secrets (passwords, API keys, certificates) have already been provisioned. The examples focus on how to reference these secrets in pipeline configurations.

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Why Use Local Secrets?

• No Hard-Coded Credentials: Keep secrets out of version control
• Environment Flexibility: Use different credentials for dev/staging/prod
• Simple Setup: No external dependencies or infrastructure required
• Platform Native: Works with systemd, Docker, Kubernetes

---

Environment Variable Interpolation

Expanso Edge supports environment variable interpolation using the ${VAR_NAME} syntax in pipeline configurations.

Basic Example

pipeline.yaml

input:
  kafka:
    addresses:
      - kafka.example.com:9092
    topics:
      - orders
    consumer_group: edge-processor
    sasl:
      mechanism: PLAIN
      user: ${KAFKA_USERNAME}
      password: ${KAFKA_PASSWORD}

output:
  http_client:
    url: https://api.example.com/ingest
    headers:
      Authorization: Bearer ${API_TOKEN}

Providing Variables

Local development:

export KAFKA_USERNAME="[email protected]"
export KAFKA_PASSWORD="secure-password"
export API_TOKEN="your-api-token"

expanso-edge run --config pipeline.yaml

Environment file:

# /etc/expanso/pipeline.env
KAFKA_USERNAME=[email protected]
KAFKA_PASSWORD=secure-password
API_TOKEN=your-api-token

# Load and run
source /etc/expanso/pipeline.env
expanso-edge run --config pipeline.yaml

---

Integration Patterns

Systemd Services

Use EnvironmentFile directive to load secrets:

/etc/systemd/system/expanso-edge.service

[Unit]
Description=Expanso Edge Node
After=network.target

[Service]
# Load pipeline secrets from environment file
EnvironmentFile=-/etc/expanso/pipeline.env

ExecStart=/usr/local/bin/expanso-edge run \
  --config /etc/expanso/pipeline.yaml

Restart=unless-stopped
User=expanso

[Install]
WantedBy=multi-user.target

Create environment file:

sudo tee /etc/expanso/pipeline.env > /dev/null << 'EOF'
[email protected]
KAFKA_PASSWORD=secure-password
API_TOKEN=your-api-token
EOF

sudo chmod 600 /etc/expanso/pipeline.env
sudo chown expanso:expanso /etc/expanso/pipeline.env

---

Docker Containers

Environment Variables

docker run -d \
  --name expanso-edge \
  -e KAFKA_USERNAME="[email protected]" \
  -e KAFKA_PASSWORD="secure-password" \
  -e API_TOKEN="your-api-token" \
  -v $(pwd)/pipeline.yaml:/etc/expanso/pipeline.yaml:ro \
  ghcr.io/expanso-io/expanso-edge:latest \
  run --config /etc/expanso/pipeline.yaml

Environment File

# Create .env file
cat > pipeline.env << 'EOF'
[email protected]
KAFKA_PASSWORD=secure-password
API_TOKEN=your-api-token
EOF

# Run with env file
docker run -d \
  --name expanso-edge \
  --env-file pipeline.env \
  -v $(pwd)/pipeline.yaml:/etc/expanso/pipeline.yaml:ro \
  ghcr.io/expanso-io/expanso-edge:latest \
  run --config /etc/expanso/pipeline.yaml

---

Kubernetes Deployments

ConfigMap for Non-Sensitive Config + Secrets for Credentials

Create the Secret:

apiVersion: v1
kind: Secret
metadata:
  name: pipeline-credentials
  namespace: expanso-system
type: Opaque
stringData:
  KAFKA_USERNAME: "[email protected]"
  KAFKA_PASSWORD: "secure-password"
  API_TOKEN: "your-api-token"

Create the Deployment:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: expanso-edge
  namespace: expanso-system
spec:
  replicas: 1
  selector:
    matchLabels:
      app: expanso-edge
  template:
    metadata:
      labels:
        app: expanso-edge
    spec:
      containers:
      - name: expanso-edge
        image: ghcr.io/expanso-io/expanso-edge:latest
        args:
          - run
          - --config
          - /etc/expanso/pipeline.yaml
        envFrom:
          - secretRef:
              name: pipeline-credentials
        volumeMounts:
          - name: pipeline-config
            mountPath: /etc/expanso
            readOnly: true
      volumes:
      - name: pipeline-config
        configMap:
          name: expanso-pipeline-config

Create Kubernetes secret:

kubectl create secret generic pipeline-credentials \
  --from-literal=KAFKA_USERNAME='[email protected]' \
  --from-literal=KAFKA_PASSWORD='secure-password' \
  --from-literal=API_TOKEN='your-api-token' \
  --namespace=expanso-system

---

File-Based Secrets

Some credentials work better as files (TLS certificates, SSH keys).

TLS Certificates Example

pipeline.yaml

output:
  http_client:
    url: https://api.example.com/ingest
    tls:
      enabled: true
      root_cas_file: /etc/expanso/certs/ca.crt
      client_certs:
        - cert_file: /etc/expanso/certs/client.crt
          key_file: /etc/expanso/certs/client.key

Mounting Files

Docker:

docker run -d \
  --name expanso-edge \
  -v $(pwd)/certs:/etc/expanso/certs:ro \
  -v $(pwd)/pipeline.yaml:/etc/expanso/pipeline.yaml:ro \
  ghcr.io/expanso-io/expanso-edge:latest \
  run --config /etc/expanso/pipeline.yaml

Kubernetes:

volumes:
- name: tls-certs
  secret:
    secretName: expanso-tls-certs
    defaultMode: 0400

volumeMounts:
- name: tls-certs
  mountPath: /etc/expanso/certs
  readOnly: true

---

Common Patterns

Database Credentials

output:
  sql_insert:
    driver: postgres
    dsn: "postgres://${DB_USER}:${DB_PASSWORD}@${DB_HOST}:5432/${DB_NAME}?sslmode=require"
    table: events
    columns: ["id", "timestamp", "data"]
    args_mapping: |
      root = [
        this.id,
        this.timestamp,
        this.data.encode("json")
      ]

API Authentication

output:
  http_client:
    url: ${API_ENDPOINT}/events
    headers:
      Authorization: Bearer ${API_TOKEN}
      X-API-Key: ${API_KEY}
    verb: POST

Message Queue Credentials

input:
  kafka:
    addresses: ["${KAFKA_BROKER}"]
    topics: ["${KAFKA_TOPIC}"]
    consumer_group: ${KAFKA_CONSUMER_GROUP}
    sasl:
      mechanism: ${KAFKA_SASL_MECHANISM}  # e.g., PLAIN, SCRAM-SHA-256
      user: ${KAFKA_USERNAME}
      password: ${KAFKA_PASSWORD}

---

Best Practices

1. Use Descriptive Variable Names

✅ Good:

POSTGRES_PASSWORD=secret
KAFKA_SASL_USERNAME=producer
API_TOKEN=abc123

❌ Bad:

PASS=secret
USER1=producer
TOKEN=abc123

2. Never Commit Secrets to Version Control

Add environment files to .gitignore:

# .gitignore
.env
*.env
pipeline.env
secrets/

3. Restrict File Permissions

chmod 600 /etc/expanso/pipeline.env
chown expanso:expanso /etc/expanso/pipeline.env

4. Separate Environments

Use different environment files per environment:

/etc/expanso/
  ├── pipeline.yaml
  ├── dev.env
  ├── staging.env
  └── prod.env

5. Document Required Variables

Create a template showing required variables:

# pipeline.env.template
KAFKA_USERNAME=
KAFKA_PASSWORD=
API_TOKEN=
DB_HOST=
DB_PASSWORD=

6. Validate Variables at Startup

Check for missing variables before running:

#!/bin/bash
REQUIRED_VARS="KAFKA_USERNAME KAFKA_PASSWORD API_TOKEN"

for var in $REQUIRED_VARS; do
  if [ -z "${!var}" ]; then
    echo "Error: $var is not set"
    exit 1
  fi
done

expanso-edge run --config pipeline.yaml

---

Limitations

When to Use External Secrets Instead

Local secrets work well for:

• Development and testing
• Small-scale deployments
• Single-node installations

Consider External Secret Managers when you need:

• Automated rotation: Credentials expire and renew automatically
• Centralized management: Hundreds of credentials across many nodes
• Audit trails: Track who accessed which secrets when
• Dynamic secrets: Generate short-lived credentials on demand
• Compliance: Meet regulatory requirements (SOC 2, HIPAA, PCI-DSS)

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Troubleshooting

Variable Not Interpolated

Symptom: Literal string ${VAR_NAME} appears in logs

Cause: Variable not set in environment

Solution:

# Check if variable is set
echo $VAR_NAME

# Set missing variable
export VAR_NAME="value"

Permission Denied Reading File

Symptom: Error: permission denied: /etc/expanso/certs/client.key

Solution:

# Fix file permissions
sudo chmod 600 /etc/expanso/certs/client.key
sudo chown expanso:expanso /etc/expanso/certs/client.key

Environment File Not Loaded

Symptom: Variables not available in systemd service

Solution: Verify EnvironmentFile path in service:

sudo systemctl cat expanso-edge | grep EnvironmentFile
sudo systemctl daemon-reload
sudo systemctl restart expanso-edge

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Next Steps

• Need audit trails? Review External Secret Managers
• Setting up bootstrap? See Bootstrapping Secrets
• Component documentation: Check component references for secret field details