High Availability and Disaster Recovery

Implement HA Jenkins architecture: (1) Deploy on Kubernetes for automatic failover: Jenkins runs in StatefulSet with persistent volume for data. (2) Use a load balancer: HAProxy or AWS ALB routes traffic to multiple Jenkins instances. (3) Implement shared state: all Jenkins instances share JENKINS_HOME on NFS or EBS volume. (4) Use read replicas: one primary writes, standby reads. Jenkins HA plugin enables failover. (5) Database-backed configuration: store job configs, credentials in database (MySQL, PostgreSQL) instead of filesystem. (6) Automated health checks: load balancer health check ensures only healthy instances receive traffic. (7) Implement graceful shutdown: running builds drain before instance goes offline. (8) Use session replication: Tomcat session data replicated across instances so users stay logged in. (9) Deploy in multiple AZs: instances in different availability zones prevent single-zone failure. (10) Backup frequency: every 15 min to S3 to minimize RPO. Target: <5 min failover time, RTO <15 min. Use Terraform/Helm to codify HA setup. Monitor instance health via Prometheus/Grafana; alert on failures immediately.

Implement split-brain protection: (1) Use distributed consensus: deploy Jenkins with etcd for quorum-based leadership. (2) Implement heartbeat mechanism: instances heartbeat to coordinator service. Lost heartbeat -> failover. (3) Use fencing: if instance loses NFS connection, it self-terminates (kill -9) rather than corrupting state. (4) Implement locking: Jenkins acquires distributed lock from Consul/etcd before writing. Lock timeout prevents zombie instances. (5) Use read-only failover: secondary instance runs in read-only mode, never writes. On primary failure, operator promotes read-only to primary. (6) Implement data versioning: track version of configuration. On split-brain, validate versions before merging. (7) Use Zookeeper for leader election: external service elects single leader, others follow. (8) Monitor NFS latency: alert if response time >1 sec. If degraded, proactively failover. (9) Implement checkpoint-restore: save build state to distributed store (etcd). On failover, restore state from checkpoint. (10) Use event-sourcing: log all state changes to Kafka. Replay logs on failover. For production: use Jenkins HA plugin with external coordination service (Consul/etcd). Never rely on NFS alone for HA.

Implement immutable, airgapped backups: (1) Use incremental backups: daily full snapshot to S3, hourly incremental backups. (2) Implement retention policy: keep 7-day rolling window, monthly full backups for 1 year. (3) Test recovery: monthly drill restores from backup to isolated environment. (4) Use snapshot versioning: S3 versioning prevents accidental/malicious deletion. (5) Air-gap backups: backups stored in separate AWS account with cross-account read-only access. (6) Implement encryption: backup encrypted with KMS key, separate from production key. (7) Use immutable storage: Glacier WORM (Write-Once-Read-Many) for archives. (8) Implement backup verification: restore backup daily to temp instance, validate Jenkins starts correctly. (9) Use point-in-time recovery: backup tagged with timestamps, enable restore to specific point. (10) Implement disaster recovery playbook: document recovery steps, RTO (target 1 hour), RPO (target 1 hour). For ransomware recovery: (1) Restore from oldest unencrypted backup. (2) Cold-boot new Jenkins instance from backup. (3) Validate backups aren't encrypted before restoration. (4) Use backup immutability (WORM) to prevent encryption. In practice: use Jenkins backup plugin, configure S3 as destination, enable versioning and lifecycle policies.

Implement low-latency DR: (1) Use database replication instead of NFS: master-slave replication with sub-second lag. Store JENKINS_HOME configs in database. (2) Implement multi-region database: AWS RDS with cross-region read replica. Failover via Route53 DNS failover. (3) Use event streaming: Kafka replicates all Jenkins state changes to DR region in real-time. (4) Implement async replication: Jenkins writes locally, async replicates to DR. RTO ~5 min. (5) Use CDN for artifact delivery: artifacts cached in both regions. (6) Implement DNS failover: Route53 health checks detect primary failure, switches to standby automatically. (7) Use database backup in DR: MySQL/PostgreSQL binary logs replicate to DR. (8) Implement warm standby: DR Jenkins instance runs continuously (read-only mode), doesn't start on demand. (9) Use state machine: track pipeline execution state in distributed store, resume on failover. (10) Implement consensus across regions: Raft protocol for leader election, tolerates network latency. For implementation: use Jenkins + MySQL + Kafka + Route53. Test failover monthly. Target RTO: <5 minutes, RPO: <1 minute.

Implement fast Kubernetes failover: (1) Configure aggressive liveness probe: `livenessProbe: { httpGet: { path: '/api/json', port: 8080 }, initialDelaySeconds: 5, periodSeconds: 3, failureThreshold: 2 }` (6 sec to detect failure). (2) Use readiness probe separately: prevents traffic to unhealthy instances. (3) Implement connection draining: preStop hook gives 10 sec for connections to close: `preStop: { exec: { command: ["/bin/sh", "-c", "sleep 10"] } }`. (4) Use load balancer connection draining: ALB/HAProxy drains connections gracefully. (5) Implement session affinity: sticky sessions avoid connection bounce. (6) Use client-side retry: Jenkins CLI client retries on timeout (3 retries, exponential backoff). (7) Implement persistent connections: use long-lived webhooks instead of polling. (8) Use health check endpoint: dedicated endpoint for fast health checks. (9) Implement PodDisruptionBudget: prevent simultaneous pod evictions: `minAvailable: 1` ensures >=1 pod always running. (10) Use pod affinity: spread replicas across nodes. If node fails, only one pod affected, others still serving. For <5 sec failover: combine aggressive liveness probe (3 sec detection) + fast reschedule (1 sec) + load balancer failover (1 sec).

Implement fleet-wide disaster recovery: (1) Use immutable infrastructure: Jenkins deployed from versioned Docker image. On compromise, roll back image version instantly. (2) Implement air-gapped "break-glass" Jenkins: separate hardened instance, pre-configured credentials in secrets manager. (3) Use configuration-as-code: all Jenkins config in Git. Restore by redeploying from clean Git commit. (4) Implement supply-chain security: sign all artifacts, detect tampering. (5) Use secrets manager with audit: HashiCorp Vault logs all credential access. (6) Implement network isolation: compromised region isolated, other regions unaffected. (7) Use disaster recovery playbook: document steps for full fleet compromise. (8) Implement incident response workflow: detect -> isolate -> assess -> recover -> communicate. (9) Use compliance scanning: regular audits detect backdoors/modifications. (10) Implement emergency contacts: defined escalation path for fleet-wide incidents. Recovery steps: (1) Detect compromise via anomaly detection (unusual API calls, credential usage). (2) Immediately revoke all credentials. (3) Isolate compromised region from network. (4) Redeploy Jenkins from known-good Git commit + Docker image. (5) Restore from backup. (6) Validate build integrity (re-sign artifacts). (7) Notify teams of incident. Test quarterly via runbook exercise.

Implement 99.99% HA: (1) Multi-region active-active: Jenkins instances in 3+ regions, all serving traffic simultaneously. No single point of failure. (2) Implement quorum-based consensus: use etcd/Consul with odd number of nodes (3 or 5). (3) Automated failover: DNS/load balancer reroutes traffic in <1 sec on instance failure. (4) Implement rolling updates: deploy patches to one instance at a time, never all simultaneously. (5) Use blue-green deployment: run old/new versions in parallel, instant rollback. (6) Implement canary deployment: new version deployed to 5% of traffic, escalate if healthy. (7) Use fault-tolerant storage: Elasticsearch cluster for shared state, 3+ nodes with replication. (8) Implement distributed caching: Redis cluster across regions for session state. (9) Use load balancing algorithm: consistent hashing prevents connection thrashing. (10) Implement chaos engineering: regularly simulate failures to test resilience. For maintenance: (1) Schedule during maintenance windows (e.g., 2am Sundays). (2) Use orchestrated rolling restarts: Jenkins controller restarts while agents continue. (3) Implement graceful degradation: reduce build parallelism during maintenance. (4) Use traffic steering: shift builds to other regions during maintenance. Target: <30 min/month maintenance window. Track uptime via monitoring: Prometheus + Grafana. Alert on any component degradation.

Implement tiered HA framework: (1) Use configuration-as-code hierarchy: base config (all regions) + regional overrides (US vs EU). (2) Define SLA levels: Tier1 (99.99%) uses 3-region active-active. Tier2 (99.9%) uses single-region with standby. (3) Use Terraform modules: each SLA tier has module defining required resources. (4) Implement automated HA provisioning: pipeline detects SLA requirement, deploys appropriate setup. (5) Use managed services: AWS RDS (database HA), ElastiCache (distributed cache), managed Kubernetes for orchestration. (6) Implement monitoring per region: SLA monitoring dashboard shows uptime per region. (7) Use flexible alerting: alert thresholds scale with SLA (99.95% allows <22 min/month downtime). (8) Implement cost optimization: lower SLA tiers use cheaper resources (spot instances, shared storage). (9) Use regional failover: within-region failover for Tier2, cross-region for Tier1. (10) Document SLA tiers: teams understand which tier their Jenkins belongs to. Implementation: use Terraform workspace per region. Variable `sla_tier` determines resource count, redundancy, backup frequency. Example: US workspace sets `sla_tier = "tier1"` -> 3-region active-active. EU workspace sets `sla_tier = "tier2"` -> single region + standby.