246 lines
9.6 KiB
Markdown
246 lines
9.6 KiB
Markdown
# 🏗️ Data Center Migration
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## Migration strategies
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| Strategy | RTO | RPO | Risk | Cost | Duration | Description |
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|-----------|-----|-----|--------|---------|-------------|-------|
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| **Cold / Big Bang** | hours–days | days | High | Low | days | Shut everything down, move, power up |
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| **Phased / Wave** | minutes (per wave) | minutes | Medium | Medium | weeks–months | Workloads moved in waves |
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| **Rolling** | 0 (live) | 0 | Low | High | months | Live migration per VM/service |
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| **Parallel Run** | 0 | 0 | Low | Very high | months | Both DCs operational, gradual cutover |
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| **Pilot Light** | hours | minutes | Medium | Low | weeks | Critical services in new DC, rest migrates |
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| **Lift & Shift** | hours | minutes | Medium | Low | weeks | VMs/servers moved without configuration changes |
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| **Re-platform** | hours | minutes | Low | Medium | months | Optimization during migration (OS upgrade, resize) |
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| **Re-architect** | 0 | 0 | Low | High | months–years | Application redesigned for new platform |
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---
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## Decision tree
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```mermaid
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flowchart TD
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Start(["DC Migration"]) --> APP{"Application\nstateful?"}
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APP -->|"Yes"| DOWNTIME{"Tolerates\ndowntime?"}
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APP -->|"No"| ROLLING["Rolling / Parallel Run"]
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DOWNTIME -->|"Yes, hours+"| COLD["Cold / Big Bang\nSimplest, cheapest\nRisk: all at once"]
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DOWNTIME -->|"Yes, minutes"| PHASED["Phased / Wave\nBy application / business unit"]
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DOWNTIME -->|"No (zero downtime)"| SYNC{"Sync replication\npossible?"}
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SYNC -->|"Yes, < 100 km"| ROLLING
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SYNC -->|"No"| PARALLEL["Parallel Run\nBoth DCs active, gradual cutover"]
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ROLLING --> ROLL_HA{"VMware,\nHyper-V?"}
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ROLL_HA -->|"Yes"| VMOTION["vMotion / Storage vMotion\nLive migration, 0 downtime"]
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ROLL_HA -->|"No"| ROLL_REPL["Storage + DB replication\nGradual workload migration"]
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```
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---
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## Migration phases
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### 1. Discovery and assessment
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| Task | Tools | Output |
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|------|----------|--------|
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| HW and SW inventory | RVTools, NetBox, CMDB | Server, VM, and service list |
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| Dependency mapping | ServiceNow, AppDynamics, manual | Application dependency graph |
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| Traffic analysis | NetFlow, sFlow, vRNI | Bandwidth, latency, peak usage |
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| Performance baseline | Prometheus, Zabbix, vRealize | CPU/RAM/disk/network per workload |
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| License audit | Flexera, SAM | Licenses, support, compliance |
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**Output:** workload list with RTO/RPO, dependencies, and criticality.
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### 2. Planning
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- **Wave plan** — workload division into migration waves (10–50 VMs per wave)
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- **Dependency ordering** — DNS, NTP, LDAP, PKI first
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- **Cutover window** — time window for switching (typically weekend)
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- **Rollback plan** — conditions and procedure for reversal
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- **Test plan** — what and how to test post-migration
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- **Communication plan** — who, when, how is informed
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### 3. New DC preparation
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- **Infrastructure** — DNS, NTP, DHCP, LDAP/AD, PKI, monitoring (see [DATACENTERS.en.md](DATACENTERS.en.md) — deployment order)
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- **Network** — BGP peering, VXLAN/VLAN, firewall rules, load balancers
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- **Storage** — SAN zoning, NAS exports, Ceph cluster
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- **Virtualization** — vCenter, Hyper-V cluster, Proxmox
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### 4. Replication and synchronization
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| Layer | Method | Tools |
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|--------|--------|----------|
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| **Storage (block)** | SAN sync/async mirror, LUN replication | NetApp SnapMirror, Dell EMC RecoverPoint, Pure ActiveCluster |
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| **Storage (file)** | DFS-R, rsync, robocopy | Windows DFS, Rsync |
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| **Storage (object)** | Cross-region replication | MinIO replication, S3 CRR |
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| **Databases** | Log shipping, CDC, streaming replication | PostgreSQL Patroni, Oracle Data Guard, MSSQL AlwaysOn, MySQL Group Replication |
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| **VM** | Storage vMotion, replication | VMware vSphere Replication, Hyper-V Replica, Zerto |
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| **Kubernetes** | Velero + Restic, Rook Ceph mirror | Velero, Rook |
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### 5. Workload migration
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#### Wave migration (recommended for medium/large DCs)
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```mermaid
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gantt
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title Wave migration
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dateFormat YYYY-MM-DD
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section Wave 1 - Core
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DNS, NTP, LDAP :done, w1a, 2026-07-01, 3d
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Monitoring + logging :done, w1b, after w1a, 2d
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section Wave 2 - Network
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Load balancers :active, w2a, 2026-07-06, 2d
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Firewalls :active, w2b, 2026-07-08, 2d
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section Wave 3 - Storage
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NAS migration :w3a, 2026-07-10, 5d
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SAN replication :w3b, 2026-07-10, 3d
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section Wave 4 - Dev/Test
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Dev VMs :w4a, 2026-07-15, 5d
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section Wave 5 - Prod tier 3
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Internal apps :w5a, 2026-07-22, 5d
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section Wave 6 - Prod tier 2
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Business apps :w6a, 2026-07-29, 5d
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section Wave 7 - Prod tier 1
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Critical apps :w7a, 2026-08-05, 5d
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```
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#### Typical single wave procedure:
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1. **Day -7**: Sync data replication (initial seed)
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2. **Day -1**: Incremental sync, final test
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3. **Day 0 (cutover)**:
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- Stop application in source DC
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- Final sync (last delta)
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- Start application in target DC
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- DNS/Traffic switch
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- Smoke test
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4. **Day +1**: Monitoring (performance, errors, lag)
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5. **Day +7**: Rollback window end (success confirmation)
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### 6. Network strategies
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#### IP re-addressing
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| Approach | Description | Pros | Cons |
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|---------|-------|--------|----------|
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| **Keep IP** | Same IPs, BGP anycast or stretch VLAN | No application config changes | Stretched VLAN/L2 limitations |
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| **Change IP** | New IP range, DNS/BGP routing change | Clean architecture | Config changes, DNS TTL |
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| **NAT translation** | NAT between old and new IP space | No application changes | Latency, troubleshooting complexity |
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**Keep IP** is only possible with:
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- L2 stretch between DCs (VXLAN, OTV) — distance limited
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- BGP anycast for VIPs (load balancers)
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- Applications tolerant to ARP cache changes
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#### DNS cutover
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```
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1. Lower TTL to 60–300 s (one week ahead)
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2. At cutover, change A/AAAA records to new IPs
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3. Wait for propagation (per TTL)
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4. Monitor traffic
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```
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#### Traffic steering
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| Technique | Use case |
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|----------|----------|
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| **BGP** | Change AS path / local pref for traffic steering |
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| **DNS** | Lower TTL, change A records |
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| **Load balancer** | Change pool members, health check |
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| **GSLB** | Global Server Load Balancing (F5 GTM, NSX ALB) |
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| **Cloud DNS** | AWS Route53, Azure Traffic Manager, Google Cloud DNS |
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### 7. Database migration
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See individual DB files for details. Summary table:
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| DB | Method | RPO | RTO | Note |
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|----|--------|-----|-----|----------|
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| **PostgreSQL** | Streaming replication + Patroni switchover | 0 (sync) / ~MB (async) | min | Patroni auto-failover |
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| **MySQL** | Group Replication / async replication | 0 (sync) / seconds | min | InnoDB Cluster |
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| **Oracle** | Data Guard switchover | 0 (sync) | min | Far sync for remote DCs |
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| **MSSQL** | AlwaysOn AG failover | 0 (sync) | min | Cloud witness |
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| **MongoDB** | Replica set election | seconds | < 1 min | Priority-based failover |
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| **Cassandra** | Multi-DC replication | eventual | 0 | Native multi-master |
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### 8. Testing
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| Phase | What to test | Method |
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|------|-------------|--------|
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| **Pre-migration** | Application in new DC (isolated) | Dry run on replicated data |
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| **Cutover** | Functionality, availability, latency | Smoke test, synthetic transactions |
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| **Post-migration** | Performance, integration, monitoring | A/B comparison with baseline, canary traffic |
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| **Rollback** | Return to old DC | Tested rollback plan |
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### 9. Rollback plan
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Each wave must have a defined rollback:
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| Condition | Action |
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|----------|------|
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| Application fails to start in new DC | DNS switch back, stop replication |
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| Performance worse than baseline (> 20 %) | Rollback, root cause analysis |
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| Integration failure (API timeout, DB connection) | Rollback, dependency check |
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| Security incident | Rollback, forensic analysis |
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Rollback must be tested **before** the real cutover.
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---
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## Special cases
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### Mainframe migration
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- **IBM z/OS** — GDPS (Geographically Dispersed Parallel Sysplex)
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- HyperSwap for storage mirroring
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- Cross-system coupling facility (XCF)
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- Often the last migrated component
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### COTS applications (Oracle EBS, SAP)
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- Require vendor-specific migration procedures
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- Oracle EBS: Autoconfig, cloning (ADXLC)
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- SAP: System Copy (Homogeneous / Heterogeneous), SWPM, SUM
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- License re-licensing on HW change
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### Cloud migration (On-prem → Cloud)
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See [CLOUD.en.md](CLOUD.en.md) — migration strategies (6 Rs):
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| Strategy | Description |
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|-----------|-------|
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| **Re-host (Lift & Shift)** | VM → Cloud VM (AWS MGN, Azure Migrate) |
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| **Re-platform** | OS upgrade, managed DB (RDS, Cloud SQL) |
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| **Re-architect** | Application rewritten as cloud-native |
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| **Retire** | Decommission unnecessary applications |
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| **Retain** | Application stays on-prem (review later) |
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| **Repurchase** | SaaS replacement |
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---
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## Recommended approach per DC size
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| DC Size | VM Count | Recommended strategy | Duration | Team |
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|-------------|----------|---------------------|-------------|-----|
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| **Small** | < 50 | Big Bang (weekend) | 2–4 days | 3–5 people |
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| **Medium** | 50–500 | Phased (5–10 waves) | 2–8 weeks | 5–10 people |
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| **Large** | 500–5000 | Phased + Rolling | 3–12 months | 10–30 people |
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| **Enterprise** | 5000+ | Parallel Run / Rolling | 12–36 months | 30+ people |
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---
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## Related
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- [DATACENTERS.en.md](DATACENTERS.en.md) — DC topologies, secondary DC, deployment order
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- [CLOUD.en.md](CLOUD.en.md) — cloud migration strategies (6 Rs)
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- [DR.en.md](DR.en.md) — disaster recovery, RTO/RPO
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- [NETWORKING.en.md](NETWORKING.en.md) — BGP, DNS, VXLAN, traffic steering
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- [STORAGE.en.md](STORAGE.en.md) — storage replication
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## Sources
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Links, books, and standards: [sources/infrastructure/sources.md](sources/infrastructure/sources.md)
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*Last revision: 2026-06-12* |