AWS Application Migration Service (MGN) - Technical Implementation Guide
Service Overview
AWS Application Migration Service (MGN) replicates physical or virtual servers to AWS by installing agents on source machines, continuously replicating data, and launching EC2 instances.
Core Functionality:
- Continuous replication with sub-5-minute RPO under optimal conditions
- Cutover downtime typically under 10 minutes for simple servers
- 90 days free per server, no per-server charges thereafter
Critical Failure Scenarios
Network Configuration Failures
High Severity - Service Breaking:
ECONNREFUSED 443- Firewall blocking AWS endpointsEHOSTUNREACH- Routing table corruption after network changesSSL_ERROR_SYSCALL- Corporate proxy intercepting SSL trafficUnable to resolve mgn-dr-gateway-*.elb.amazonaws.com- DNS resolution failures
Impact: Complete replication failure, requires immediate network team intervention
Agent Communication Failures
Medium Severity - Monitoring Required:
AgentNotSeen- Last heartbeat >45 minutes agoStagingAreaServerCreationFailure- Staging subnet IP exhaustionReplicationLagExceedsThreshold- Network bandwidth insufficientInsufficientDiskSpace- Staging instance storage full
Frequency: Network hiccups cause replication lag spikes lasting hours during high I/O periods
Licensing and OS Compatibility Issues
High Impact - Post-Migration:
- Windows:
Error 0xC004F074- License activation failure after hardware change - SQL Server:
Error 5808- System catalog update failures - Oracle:
ORA-00600- Hardware detection triggers internal errors
Resolution Time: License reactivation calls with vendors can take 2-4 hours
Configuration Requirements
Network Prerequisites
Required Ports: TCP 443, TCP 1500 to AWS endpoints
Staging Subnet: S3/EC2/IAM access required
Firewall: FQDN-based rules (IP ranges change frequently)
OS Support Matrix
Supported (Production Ready):
- Windows Server 2016-2022
- RHEL 7+, Ubuntu 18.04+, Amazon Linux 2
Deprecated:
- Windows Server 2003 support ends 2026
- Legacy Linux distributions (<RHEL 7) unsupported
Performance Thresholds
Replication Performance:
- Initial sync: 24-72 hours for 500GB server over 100 Mbps
- RPO: 5-15 minutes typical, sub-5-minute under perfect conditions
- Network requirement: Direct Connect recommended for 50+ servers or >2TB databases
Resource Requirements and Costs
Infrastructure Costs During Migration
| Server Size | Staging Instance | Monthly Cost | Storage Cost |
|---|---|---|---|
| Small (100GB) | t3.small | $15 | $8 |
| Medium (500GB) | t3.medium | $30 | $40 |
| Large DB (2TB) | r6i.large | $135 | $160 |
Hidden Costs:
- EBS storage: GP3 ~$0.08/GB/month, IO2 ~$0.125/GB/month
- Data transfer: Variable egress charges
- Extended migration timeframes increase staging costs
Time Investment Reality
Simple Servers (web/app tiers):
- Optimistic: 1-2 weeks
- Realistic: 6 weeks
Complex Systems (DB/AD integration):
- Minimum: 3-6 months
- Factors: Hardcoded IP addresses, custom networking, legacy dependencies
Expertise Requirements
Essential Skills:
- AWS networking (VPC, security groups, routing)
- Firewall rule management
- OS-level troubleshooting
- Vendor license reactivation processes
Decision Criteria vs Alternatives
| Factor | AWS MGN | Manual Migration | Third-Party Tools |
|---|---|---|---|
| Speed | Faster than manual, slower than advertised | Painfully slow | Tool-dependent |
| Downtime | Minutes | Hours to days | Varies wildly |
| Hidden Costs | Staging + storage + egress | Human time | Licensing fees |
| Failure Support | AWS support (paid tiers) | Self-resolution | Vendor quality varies |
| Learning Curve | AWS console + networking | Known quantity | Tool-specific |
MGN Recommended When:
10 servers to migrate
- Network bandwidth >100 Mbps
- AWS expertise available
- Budget for staging infrastructure
Avoid MGN When:
- Single server migrations
- Legacy OS requiring replacement anyway
- No AWS networking expertise
- Tight budget constraints
Implementation Best Practices
Pre-Migration Validation
Network Connectivity Test:
telnet replication-endpoint.aws.com 443 telnet replication-endpoint.aws.com 1500Agent Installation Prerequisites:
- Administrative privileges on source servers
- Antivirus exclusions for MGN agent
- Backup current server state
Staging Environment Sizing:
- Match or exceed source server specifications
- Plan for 20% storage overhead
- Configure appropriate security groups
Common Misconceptions
- "70% reduction in migration time" - Measured against manual file copies, not realistic migrations
- "Sub-minute RPO" - Requires perfect network conditions rarely achieved
- "Zero downtime migration" - DNS cutover and application startup still require downtime
Troubleshooting Sequence (3AM Debugging)
- Check MGN console agent status
- Review source server logs:
/var/log/aws_replication_installer.log - Verify network connectivity to AWS endpoints
- Check EBS volume space in staging area:
df -h - Validate security group configurations
Critical Warnings
What Official Documentation Omits
- Static routes and firewall rules don't transfer automatically
- DNS configurations require manual reconfiguration
- Application hardcoded IP addresses cause post-migration failures
- Windows license reactivation required after hardware changes
Breaking Points
- UI Performance: Debugging becomes impossible with >1000 spans in distributed transactions
- Network Dependency: Corporate proxy SSL interception breaks replication
- Storage Limits: Staging instances run out of space during high I/O periods
Migration vs Replacement Decision Matrix
Migrate:
- Applications with current vendor support
- Systems with clear dependencies mapped
- Servers running supported OS versions
Replace:
- Windows Server 2003/2008 systems
- Applications with hardcoded network configurations
- Systems requiring extensive post-migration remediation
Enterprise Features
MGN Connector (VMware Integration)
- Benefit: Automates agent deployment for vCenter 6.7+
- Limitation: Requires API access and snapshot permissions
- Use Case: >50 VMware VMs requiring migration
Wave Management
- Function: Coordinates multi-server migrations
- Critical For: Three-tier applications requiring specific startup order
- Implementation: Groups dependent servers for synchronized cutover
Organizations Integration
- Purpose: Centralized tracking across multiple AWS accounts
- Primary Users: Consulting firms managing client migrations
- Value: Limited for single-organization migrations
Resource Links
Troubleshooting Resources
- AWS MGN Troubleshooting Guide - 3AM debugging reference
- Common Replication Errors - Error code dictionary
- AWS re:Post MGN Forum - Real user experiences
Cost Management
- AWS Simple Monthly Calculator - Pre-migration cost estimation
- EBS Pricing Details - Storage cost breakdown
- Data Transfer Pricing - Egress charge explanation
Implementation Guidance
- Network Requirements - Firewall rule specifications
- VMware Agentless Setup - vCenter integration troubleshooting
- Launch Settings Configuration - Post-migration instance configuration
Useful Links for Further Investigation
Resources That Actually Help When Things Break
| Link | Description |
|---|---|
| AWS MGN User Guide | The official docs - actually decent compared to most AWS services, but the troubleshooting section assumes you have psychic powers for diagnosing network issues. |
| MGN API Reference | API docs that are useful if you're automating this stuff. Way better than clicking through the console 500 times, though the error responses could be more helpful. |
| Migration Hub Dashboard | Tracks migration progress better than spreadsheets, which isn't saying much. At least you can see when stuff breaks without SSH'ing into every server. |
| MGN Pricing Page | Where you learn that "free" means "free service, but you still pay for all the AWS infrastructure." Use this before your CFO asks why the AWS bill tripled. |
| AWS MGN Technical Training | Free course that covers the basics without too much marketing fluff. Skip to the hands-on labs - that's where you learn what actually breaks. |
| Architecture Blog Posts | Real-world examples from people who've done this before. Much more useful than vendor whitepapers that assume your environment is perfect. |
| Migration Acceleration Program | AWS consulting that might actually help if you're migrating 100+ servers. Less useful for smaller migrations where you just need the tool to work. |
| Prescriptive Guidance for MGN | Architecture advice that's actually practical. Covers the gotchas they don't mention in the sales pitch. |
| Migration Factory Solution | Automation tools for large migrations. Overkill for small shops, essential if you're migrating entire data centers and need to track everything. |
| Well-Architected Migration Lens | Best practices that assume you have time to do things right. Good checklist, but real migrations are messier than this suggests. |
| MGN Service Overview | Marketing page, but has useful getting-started links when you need to show someone what this tool actually does. |
| AWS re:Post MGN Forum | Where you find answers to questions like "why did replication stop working after a Windows update?" Real user experiences, not just vendor docs. |
| AWS Support Options | Professional support that's actually helpful for MGN issues, unlike some AWS services. Worth it if you're migrating production workloads. |
| AWS Migration Partners | Directory of consultants who know MGN. Quality varies wildly - ask for references and actual migration experience, not just certifications. |
| TEKsystems Migration Services | Professional services option if you need someone else to handle the migration. Expensive but they know the common failure modes. |
| MGN Release Notes | Bug fixes and new features. Read these - sometimes they fix the exact issue that's been driving you crazy. |
| AWS What's New for MGN | New capabilities and service updates. The important stuff gets buried in here, so check monthly. |
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