Schema Registry Operations

Operational procedures for running AxonOps Schema Registry in production environments.

AxonOps Schema Registry is a high-performance, API-compatible Kafka Schema Registry written in Go. It provides a drop-in replacement for Confluent Schema Registry with enterprise features and flexible storage backends.

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Why AxonOps Schema Registry

Feature	AxonOps	Confluent OSS	Confluent Enterprise
License	Apache 2.0	Community	Commercial
Language	Go	Java	Java
API Compatible	✅	N/A	N/A
PostgreSQL Backend	✅	❌	❌
MySQL Backend	✅	❌	❌
Cassandra Backend	✅	❌	❌
No Kafka Dependency	✅	❌	❌
Basic Auth	✅	❌	✅
API Keys	✅	❌	✅
LDAP/AD	✅	❌	✅
OIDC	✅	❌	✅
RBAC	✅	❌	✅
Audit Logging	✅	❌	✅
Single Binary	✅	❌	❌
Memory Footprint	~50MB	~500MB+	~500MB+

---

Deployment

Single Node (Development)

For development and testing with in-memory storage:

# Docker - in-memory storage
docker run -d -p 8081:8081 ghcr.io/axonops/axonops-schema-registry:latest

Verify deployment:

curl http://localhost:8081/
# Response: {}

Production with PostgreSQL

PostgreSQL provides a reliable backend for single-datacenter production deployments:

docker run -d -p 8081:8081 \
  -e STORAGE_TYPE=postgresql \
  -e POSTGRES_HOST=postgres.example.com \
  -e POSTGRES_PORT=5432 \
  -e POSTGRES_USER=schemaregistry \
  -e POSTGRES_PASSWORD=secret \
  -e POSTGRES_DATABASE=schemaregistry \
  -e POSTGRES_SSLMODE=require \
  ghcr.io/axonops/axonops-schema-registry:latest

Configuration file:

# config.yaml
server:
  host: 0.0.0.0
  port: 8081

storage:
  type: postgresql
  postgresql:
    host: postgres.example.com
    port: 5432
    user: schemaregistry
    password: secret
    database: schemaregistry
    sslmode: require

Production with MySQL

docker run -d -p 8081:8081 \
  -e STORAGE_TYPE=mysql \
  -e MYSQL_HOST=mysql.example.com \
  -e MYSQL_PORT=3306 \
  -e MYSQL_USER=schemaregistry \
  -e MYSQL_PASSWORD=secret \
  -e MYSQL_DATABASE=schemaregistry \
  ghcr.io/axonops/axonops-schema-registry:latest

Multi-Datacenter with Cassandra

For globally distributed deployments, Cassandra provides active-active replication:

Configuration:

# config.yaml
storage:
  type: cassandra
  cassandra:
    hosts:
      - cassandra1.dc1.example.com
      - cassandra2.dc1.example.com
      - cassandra3.dc1.example.com
    keyspace: schema_registry
    replication_factor: 3
    consistency_level: LOCAL_QUORUM
    username: schemaregistry
    password: secret

High Availability Architecture

Docker Compose

version: '3.8'
services:
  schema-registry:
    image: ghcr.io/axonops/axonops-schema-registry:latest
    hostname: schema-registry
    ports:
      - "8081:8081"
    environment:
      # Storage
      STORAGE_TYPE: postgresql
      POSTGRES_HOST: postgres
      POSTGRES_PORT: 5432
      POSTGRES_USER: schemaregistry
      POSTGRES_PASSWORD: secret
      POSTGRES_DATABASE: schemaregistry

      # Server
      SERVER_HOST: 0.0.0.0
      SERVER_PORT: 8081

      # Compatibility
      COMPATIBILITY_LEVEL: BACKWARD
    healthcheck:
      test: ["CMD", "curl", "-f", "http://localhost:8081/"]
      interval: 30s
      timeout: 10s
      retries: 5
    depends_on:
      - postgres

  postgres:
    image: postgres:16
    environment:
      POSTGRES_USER: schemaregistry
      POSTGRES_PASSWORD: secret
      POSTGRES_DB: schemaregistry
    volumes:
      - postgres_data:/var/lib/postgresql/data

volumes:
  postgres_data:

Kubernetes Deployment

apiVersion: apps/v1
kind: Deployment
metadata:
  name: schema-registry
spec:
  replicas: 3
  selector:
    matchLabels:
      app: schema-registry
  template:
    metadata:
      labels:
        app: schema-registry
    spec:
      containers:
        - name: schema-registry
          image: ghcr.io/axonops/axonops-schema-registry:latest
          ports:
            - containerPort: 8081
          env:
            - name: STORAGE_TYPE
              value: postgresql
            - name: POSTGRES_HOST
              value: postgres.database.svc.cluster.local
            - name: POSTGRES_USER
              valueFrom:
                secretKeyRef:
                  name: schema-registry-secrets
                  key: postgres-user
            - name: POSTGRES_PASSWORD
              valueFrom:
                secretKeyRef:
                  name: schema-registry-secrets
                  key: postgres-password
            - name: POSTGRES_DATABASE
              value: schemaregistry
          resources:
            requests:
              memory: "64Mi"
              cpu: "100m"
            limits:
              memory: "128Mi"
              cpu: "500m"
          livenessProbe:
            httpGet:
              path: /
              port: 8081
            initialDelaySeconds: 10
            periodSeconds: 10
          readinessProbe:
            httpGet:
              path: /
              port: 8081
            initialDelaySeconds: 5
            periodSeconds: 5
---
apiVersion: v1
kind: Service
metadata:
  name: schema-registry
spec:
  selector:
    app: schema-registry
  ports:
    - port: 8081
      targetPort: 8081
  type: ClusterIP

Package Installation

Debian/Ubuntu (APT):

# Add repository
curl -fsSL https://packages.axonops.com/gpg.key | sudo gpg --dearmor -o /usr/share/keyrings/axonops-archive-keyring.gpg
echo "deb [signed-by=/usr/share/keyrings/axonops-archive-keyring.gpg] https://packages.axonops.com/apt stable main" | sudo tee /etc/apt/sources.list.d/axonops.list

# Install
sudo apt update
sudo apt install axonops-schema-registry

RHEL/CentOS (YUM):

# Add repository
cat << 'EOF' | sudo tee /etc/yum.repos.d/axonops.repo
[axonops]
name=AxonOps Repository
baseurl=https://packages.axonops.com/yum
enabled=1
gpgcheck=1
gpgkey=https://packages.axonops.com/gpg.key
EOF

# Install
sudo yum install axonops-schema-registry

---

Configuration

Essential Settings

Property	Environment Variable	Default	Description
server.host	SERVER_HOST	0.0.0.0	Bind address
server.port	SERVER_PORT	8081	Listen port
storage.type	STORAGE_TYPE	memory	Backend: memory, postgresql, mysql, cassandra
compatibility.level	COMPATIBILITY_LEVEL	BACKWARD	Default compatibility

Storage Configuration

=== "PostgreSQL"

```yaml
storage:
  type: postgresql
  postgresql:
    host: localhost
    port: 5432
    user: schemaregistry
    password: secret
    database: schemaregistry
    sslmode: disable  # disable, require, verify-ca, verify-full
    max_connections: 25
    connection_timeout: 30s
```

=== "MySQL"

```yaml
storage:
  type: mysql
  mysql:
    host: localhost
    port: 3306
    user: schemaregistry
    password: secret
    database: schemaregistry
    tls: false
    max_connections: 25
```

=== "Cassandra"

```yaml
storage:
  type: cassandra
  cassandra:
    hosts:
      - cassandra1:9042
      - cassandra2:9042
    keyspace: schema_registry
    replication_factor: 3
    consistency_level: LOCAL_QUORUM
    username: schemaregistry
    password: secret
```

Security Configuration

TLS/HTTPS:

server:
  tls:
    enabled: true
    cert_file: /etc/schema-registry/tls/server.crt
    key_file: /etc/schema-registry/tls/server.key
    ca_file: /etc/schema-registry/tls/ca.crt  # for mTLS
    client_auth: require  # none, request, require

Basic Authentication:

auth:
  type: basic
  basic:
    users:
      - username: admin
        password: $2a$10$...  # bcrypt hash
        roles: [admin]
      - username: developer
        password: $2a$10$...
        roles: [developer]

API Keys:

auth:
  type: apikey
  apikey:
    keys:
      - key: sk_live_...
        name: production-app
        roles: [developer]
        expires_at: 2025-12-31T23:59:59Z

LDAP/Active Directory:

auth:
  type: ldap
  ldap:
    url: ldaps://ldap.example.com:636
    bind_dn: cn=service,dc=example,dc=com
    bind_password: secret
    base_dn: ou=users,dc=example,dc=com
    user_filter: (uid={0})
    group_filter: (member={0})
    role_mapping:
      cn=schema-admins,ou=groups,dc=example,dc=com: admin
      cn=developers,ou=groups,dc=example,dc=com: developer

OpenID Connect (OIDC):

auth:
  type: oidc
  oidc:
    issuer_url: https://auth.example.com
    client_id: schema-registry
    client_secret: secret
    scopes: [openid, profile, email]
    role_claim: groups
    role_mapping:
      schema-admins: admin
      developers: developer

Role-Based Access Control (RBAC)

rbac:
  roles:
    admin:
      permissions:
        - resource: "*"
          actions: ["*"]
    developer:
      permissions:
        - resource: "subjects/*"
          actions: [read, write]
        - resource: "compatibility"
          actions: [read]
    readonly:
      permissions:
        - resource: "subjects/*"
          actions: [read]
        - resource: "schemas/*"
          actions: [read]

Audit Logging

audit:
  enabled: true
  log_file: /var/log/schema-registry/audit.log
  include:
    - schema_registered
    - schema_deleted
    - compatibility_changed
    - auth_success
    - auth_failure

---

Monitoring

Health Check

# Basic health check
curl http://schema-registry:8081/
# Response: {}

# With authentication
curl -u admin:password http://schema-registry:8081/

Prometheus Metrics

AxonOps Schema Registry exposes Prometheus metrics:

# Enable metrics
metrics:
  enabled: true
  path: /metrics
  port: 9090  # separate port, or use main port

Key metrics:

Metric	Description
schema_registry_requests_total	Total API requests by endpoint and status
schema_registry_request_duration_seconds	Request latency histogram
schema_registry_schemas_total	Total registered schemas
schema_registry_subjects_total	Total subjects
schema_registry_storage_operations_total	Storage backend operations
schema_registry_storage_operation_duration_seconds	Storage operation latency

Prometheus scrape config:

scrape_configs:
  - job_name: 'schema-registry'
    static_configs:
      - targets: ['schema-registry:8081']
    metrics_path: /metrics

Grafana Dashboard

Key panels to include:

• Request rate by endpoint
• Error rate (4xx, 5xx responses)
• Request latency (p50, p95, p99)
• Schema registration rate
• Storage backend health
• Memory and CPU usage

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Backup and Recovery

Database Backup

Since AxonOps Schema Registry uses standard databases, leverage native backup tools:

PostgreSQL:

# Backup
pg_dump -h postgres -U schemaregistry schemaregistry > schemas-backup.sql

# Restore
psql -h postgres -U schemaregistry schemaregistry < schemas-backup.sql

MySQL:

# Backup
mysqldump -h mysql -u schemaregistry -p schemaregistry > schemas-backup.sql

# Restore
mysql -h mysql -u schemaregistry -p schemaregistry < schemas-backup.sql

Cassandra:

# Backup using nodetool snapshot
nodetool snapshot -t schema_registry_backup schema_registry

API-Based Backup

Export all schemas via REST API:

#!/bin/bash
# backup-schemas.sh

REGISTRY_URL="http://schema-registry:8081"
BACKUP_DIR="./schema-backup-$(date +%Y%m%d)"

mkdir -p "$BACKUP_DIR"

# Get all subjects
SUBJECTS=$(curl -s "$REGISTRY_URL/subjects" | jq -r '.[]')

for SUBJECT in $SUBJECTS; do
  echo "Backing up: $SUBJECT"

  # Get all versions
  VERSIONS=$(curl -s "$REGISTRY_URL/subjects/$SUBJECT/versions" | jq -r '.[]')

  for VERSION in $VERSIONS; do
    curl -s "$REGISTRY_URL/subjects/$SUBJECT/versions/$VERSION" \
      > "$BACKUP_DIR/${SUBJECT}_v${VERSION}.json"
  done

  # Backup compatibility config
  curl -s "$REGISTRY_URL/config/$SUBJECT" \
    > "$BACKUP_DIR/${SUBJECT}_config.json" 2>/dev/null || true
done

# Backup global config
curl -s "$REGISTRY_URL/config" > "$BACKUP_DIR/_global_config.json"

echo "Backup complete: $(ls "$BACKUP_DIR" | wc -l) files"

Recovery

#!/bin/bash
# restore-schemas.sh

REGISTRY_URL="http://schema-registry:8081"
BACKUP_DIR="$1"

if [ -z "$BACKUP_DIR" ]; then
  echo "Usage: $0 <backup-directory>"
  exit 1
fi

# Restore global config
if [ -f "$BACKUP_DIR/_global_config.json" ]; then
  COMPAT=$(cat "$BACKUP_DIR/_global_config.json" | jq -r '.compatibilityLevel')
  curl -X PUT \
    -H "Content-Type: application/vnd.schemaregistry.v1+json" \
    -d "{\"compatibility\": \"$COMPAT\"}" \
    "$REGISTRY_URL/config"
fi

# Restore schemas (sorted by version)
for FILE in $(ls "$BACKUP_DIR"/*_v*.json | sort -t'v' -k2 -n); do
  SUBJECT=$(basename "$FILE" | sed 's/_v[0-9]*\.json//')
  SCHEMA=$(cat "$FILE" | jq '.schema')
  SCHEMA_TYPE=$(cat "$FILE" | jq -r '.schemaType // "AVRO"')

  echo "Restoring: $SUBJECT"

  curl -X POST \
    -H "Content-Type: application/vnd.schemaregistry.v1+json" \
    -d "{\"schema\": $SCHEMA, \"schemaType\": \"$SCHEMA_TYPE\"}" \
    "$REGISTRY_URL/subjects/$SUBJECT/versions"
done

---

Administration

Subject Management

# List all subjects
curl http://schema-registry:8081/subjects

# Get subject versions
curl http://schema-registry:8081/subjects/my-topic-value/versions

# Get latest schema
curl http://schema-registry:8081/subjects/my-topic-value/versions/latest

# Delete subject (soft delete)
curl -X DELETE http://schema-registry:8081/subjects/my-topic-value

# Delete subject (permanent)
curl -X DELETE "http://schema-registry:8081/subjects/my-topic-value?permanent=true"

Schema Management

# Register a new schema
curl -X POST \
  -H "Content-Type: application/vnd.schemaregistry.v1+json" \
  -d '{"schema": "{\"type\": \"record\", \"name\": \"User\", \"fields\": [{\"name\": \"id\", \"type\": \"int\"}]}"}' \
  http://schema-registry:8081/subjects/users-value/versions

# Get schema by ID
curl http://schema-registry:8081/schemas/ids/1

# Check schema compatibility
curl -X POST \
  -H "Content-Type: application/vnd.schemaregistry.v1+json" \
  -d '{"schema": "{...}"}' \
  http://schema-registry:8081/compatibility/subjects/users-value/versions/latest

Compatibility Management

# Get global compatibility level
curl http://schema-registry:8081/config
# Response: {"compatibilityLevel": "BACKWARD"}

# Set global compatibility
curl -X PUT \
  -H "Content-Type: application/vnd.schemaregistry.v1+json" \
  -d '{"compatibility": "FULL"}' \
  http://schema-registry:8081/config

# Set subject-level compatibility
curl -X PUT \
  -H "Content-Type: application/vnd.schemaregistry.v1+json" \
  -d '{"compatibility": "NONE"}' \
  http://schema-registry:8081/config/my-topic-value

# Delete subject-level config (revert to global)
curl -X DELETE http://schema-registry:8081/config/my-topic-value

Mode Management

# Get current mode
curl http://schema-registry:8081/mode
# Response: {"mode": "READWRITE"}

# Set read-only mode (maintenance)
curl -X PUT \
  -H "Content-Type: application/vnd.schemaregistry.v1+json" \
  -d '{"mode": "READONLY"}' \
  http://schema-registry:8081/mode

# Set import mode (for restore with specific IDs)
curl -X PUT \
  -H "Content-Type: application/vnd.schemaregistry.v1+json" \
  -d '{"mode": "IMPORT"}' \
  http://schema-registry:8081/mode

Mode	Description
READWRITE	Normal operation
READONLY	Maintenance mode, reject writes
IMPORT	Allow schema registration with specific IDs

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Troubleshooting

Common Issues

Issue	Cause	Solution
409 Conflict	Incompatible schema	Check compatibility mode, review schema changes
401 Unauthorized	Authentication failure	Verify credentials, check auth configuration
403 Forbidden	Insufficient permissions	Review RBAC roles and permissions
503 Service Unavailable	Database connection failure	Check database connectivity and credentials
404 Not Found	Subject/schema doesn't exist	Verify subject name spelling

Debugging

Enable debug logging:

logging:
  level: debug
  format: json

Check storage connectivity:

# PostgreSQL
psql -h postgres -U schemaregistry -d schemaregistry -c "SELECT 1"

# MySQL
mysql -h mysql -u schemaregistry -p -e "SELECT 1"

# Cassandra
cqlsh cassandra -u schemaregistry -p password -e "SELECT * FROM schema_registry.schemas LIMIT 1"

View audit log:

tail -f /var/log/schema-registry/audit.log | jq .

Performance Issues

Symptoms: High latency, timeouts

Investigation:

# Check metrics
curl http://schema-registry:8081/metrics | grep duration

# Check database performance
# PostgreSQL
SELECT * FROM pg_stat_activity WHERE datname = 'schemaregistry';

# Check connection pool
curl http://schema-registry:8081/metrics | grep connections

Solutions:

• Increase database connection pool size
• Add read replicas for high read workloads
• Enable schema caching on clients
• Scale horizontally with more instances

---

Performance Tuning

Server Configuration

server:
  read_timeout: 30s
  write_timeout: 30s
  idle_timeout: 120s
  max_header_bytes: 1048576

Database Connection Pool

storage:
  postgresql:
    max_connections: 50
    min_connections: 10
    connection_timeout: 30s
    max_connection_lifetime: 1h

Rate Limiting

rate_limit:
  enabled: true
  requests_per_second: 1000
  burst: 100

Client Caching

Configure Kafka clients to cache schemas:

# Producer/Consumer configuration
schema.registry.url=http://schema-registry:8081
auto.register.schemas=true
schema.cache.capacity=1000

---

Capacity Planning

Metric	Small	Medium	Large
Schemas	< 1,000	1,000-10,000	> 10,000
Requests/sec	< 100	100-1,000	> 1,000
Memory	64 MB	128 MB	256+ MB
CPU	0.5 core	1-2 cores	2+ cores
Instances	1-2	2-3	3+

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Related Documentation

• Schema Registry Overview - Architecture and concepts
• Schema Evolution - Safe evolution practices
• Compatibility - Compatibility modes
• Why Schemas - Schema management benefits
• AxonOps Schema Registry GitHub