AWS Lambda Managed Instances (LMI)

Run Lambda functions on current-generation EC2 instances in your account while AWS manages provisioning, patching, scaling, routing, and load balancing. Combines Lambda's developer experience with EC2's pricing and hardware options.

For standard Lambda development, see aws-lambda skill. For SAM/CDK deployment, see aws-serverless-deployment skill.

When to Load Reference Files

• Cost comparison, pricing analysis, Lambda vs LMI cost, Savings Plans, or Reserved Instances -> see references/cost-comparison.md
• Instance types, memory sizing, vCPU ratios, scaling tuning, or capacity provider config -> see references/configuration-guide.md
• Thread safety, concurrency model, code review checklist, Powertools compatibility, or multi-concurrency readiness -> see references/thread-safety.md
• Before/after code examples, runtime-specific migration (Node.js, Python, Java, .NET), or connection pooling -> see references/migration-patterns.md
• IAM roles, VPC setup, CLI commands, SAM template, or CDK example -> see references/infrastructure-setup.md and scripts/setup-lmi.sh
• Errors, throttling, debugging, or stuck deployments -> see references/troubleshooting.md

Quick Decision: Is LMI Right for This Workload?

Signal	LMI is a strong fit	Standard Lambda is better
Traffic	Steady, predictable, 50M+ req/mo	Bursty, unpredictable, long idle
Cost	Duration-heavy spend at scale	Low or sporadic invocations
Cold starts	Unacceptable (LMI eliminates for provisioned capacity; scale-out may have brief delays)	Tolerable or mitigated by SnapStart
Compute	Latest CPUs, specific families, high network bandwidth	Standard Lambda memory/CPU sufficient
Isolation	Dedicated EC2 instances in your account, full VPC control	Shared Firecracker micro-VMs acceptable
Scale-to-zero	Not needed (execution environments always running)	Required (pay nothing when idle)
Code readiness	Thread-safe (Node.js/Java/.NET) or any Python code	Non-thread-safe Node.js/Java/.NET, expensive to change

Instructions

Step 1: Assess the Workload

Gather these signals before recommending:

1. Traffic pattern: Steady vs bursty? Requests per second?
2. Current costs: Monthly Lambda spend? Existing Savings Plans?
3. Runtime: Node.js, Java, .NET, or Python?
4. Memory/CPU: How much memory? CPU-bound or I/O-bound?
5. Execution duration: Average and P99?
6. Concurrency readiness: Thread safety (Node.js/Java/.NET)? Shared /tmp paths? Per-invocation DB connections?
7. VPC: Already in a VPC? Private resource access needed?

Step 2: Build the Cost Comparison

REQUIRED: Present a cost comparison before recommending LMI. Compare at minimum:

Scenario	When it wins
Lambda on-demand	Low volume, bursty traffic
LMI on-demand	High volume, steady traffic

Rule of thumb: LMI becomes cost-competitive when your Lambda spend exceeds ~$1,000/month with steady traffic.

For discount analysis (Savings Plans, Reserved Instances), refer users to the AWS Pricing Calculator and references/cost-comparison.md for formulas and worked examples. Discount recommendations require workload-specific forecasting beyond this skill's scope.

Step 3: Configure the Deployment

Instance families (~450 types): C-series (compute, .xlarge+), M-series (general, .large+), R-series (memory, .large+). ARM (Graviton) for best price-performance.

Memory-to-vCPU ratios: 2:1 (compute), 4:1 (general, default), 8:1 (memory). Min 2 GB, max 32 GB.

Multi-concurrency defaults/vCPU: Node.js 64, Java 32, .NET 32, Python 16.

Scaling: MinExecutionEnvironments (default 3), MaxVCpuCount (default 400), TargetResourceUtilization.

See references/configuration-guide.md for decision trees and detailed tuning.

Step 4: Migrate the Code

Review code for concurrency safety. LMI runs multiple invocations concurrently per execution environment, but the model differs by runtime:

• Python: Process-based isolation — globals are NOT shared. No thread-safety changes needed. Focus on /tmp conflicts and memory sizing (per-process × concurrency).
• Node.js: Worker threads — globals shared within a worker. Requires async safety. Callback handlers not supported on Node.js 22.
• Java/.NET: OS threads/Tasks — handler shared across threads. Requires full thread safety.

Common issues (all runtimes): shared /tmp paths, per-invocation DB connections. Thread-safety issues (Node.js/Java/.NET only): mutable globals, non-thread-safe libs.

See references/thread-safety.md for the review checklist and references/migration-patterns.md for runtime-specific before/after code.

Step 5: Set Up Infrastructure

1. Create two IAM roles: execution role (for the function) and operator role (for capacity provider EC2 management)
2. Configure VPC with subnets across multiple AZs (recommended 3+ for resiliency)
3. Create capacity provider with VPC config and scaling limits
4. Create or update function with capacity provider attachment
5. Publish a version (triggers instance provisioning)

See references/infrastructure-setup.md for CLI commands and SAM templates.

Step 6: Validate and Cut Over

1. Deploy to a non-production environment first
2. Monitor CloudWatch: CPU utilization, memory, concurrency, throttle rate
3. Gradual traffic shift with weighted aliases (10% → 50% → 100%)
4. Compare costs after 1-2 weeks of production data
5. Decommission standard Lambda once stable

Best Practices

Configuration

• Do: Start with 4:1 ratio and runtime default concurrency
• Do: Use ARM (Graviton) unless x86 dependencies exist
• Do: Let Lambda choose instance types unless specific hardware needed
• Do: Set MaxVCpuCount to control cost ceiling
• Don't: Set MinExecutionEnvironments below 3 in production (reduces multi-AZ coverage). Non-prod environments can use 1 as the minimum.
• Don't: Over-restrict instance types (lowers availability)

Migration

• Do: Start with I/O-heavy functions (benefit most from multi-concurrency; CPU-bound functions compete for same CPU)
• Do: Review code for concurrency safety before attaching to capacity provider (thread safety for Node.js/Java/.NET; /tmp and memory for Python)
• Do: Use weighted aliases for gradual traffic shift
• Do: Include request IDs in all log statements
• Do: Initialize DB pools and SDK clients outside the handler
• Do: Estimate total /tmp usage under max concurrency
• Don't: Write to hardcoded /tmp paths without request-unique naming
• Don't: Skip cost comparison — LMI is not always cheaper

Operations

• Do: Set CloudWatch alarms on throttle rate > 1% and CPU > 80%
• Don't: Manually terminate LMI EC2 instances (delete the capacity provider instead)
• Don't: Forget to publish a version — unpublished functions cannot run on LMI

Limits Quick Reference

Resource	Limit
Memory	2 GB min, 32 GB max
Concurrency/vCPU	64 (Node.js), 32 (Java/.NET), 16 (Python)
Instance lifespan	~12 hours (auto-replaced by Lambda)
EE lifespan	~4 hours (auto-replaced by Lambda)
Runtimes	Node.js, Java, .NET, Python
Instance families	C (.xlarge+), M (.large+), R (.large+)
Scaling	Doubles within 5 min without throttles

Troubleshooting Quick Reference

Issue	Cause	Fix
429 throttles	Traffic exceeds scaling speed	Increase MinExecutionEnvironments or lower TargetResourceUtilization
Function stuck PENDING	Provisioning instances	Wait; check VPC/IAM config
Architecture mismatch	Function ≠ capacity provider arch	Align both to same architecture
Cannot terminate instances	Managed by capacity provider	Delete capacity provider instead
Race conditions	Code not thread-safe	See references/thread-safety.md

See references/troubleshooting.md for detailed resolution steps.

Configuration

AWS CLI Setup

REQUIRED: AWS credentials configured on the host machine.

Verify access: Run aws sts get-caller-identity

Regional Availability

Currently available: us-east-1, us-east-2, us-west-2, ap-northeast-1, eu-west-1. Expanding to all commercial regions soon.

Check the Lambda Managed Instances documentation for the latest regional availability.

Language Selection

Default: TypeScript

Override: "use Python" → Python, "use JavaScript" → JavaScript. When not specified, ALWAYS use TypeScript.

IaC Framework Selection

Default: CDK

Override: "use SAM" → SAM YAML, "use CloudFormation" → CloudFormation YAML. When not specified, ALWAYS use CDK.

Error Scenarios

Serverless MCP Server Unavailable

• Inform user: "AWS Serverless MCP not responding"
• Ask: "Proceed without MCP support?"
• DO NOT continue without user confirmation

Unsupported Runtime

• State: "Lambda Managed Instances does not yet support [runtime]"
• List supported runtimes
• Suggest standard Lambda as alternative

Unsupported Region

• State: "Lambda Managed Instances is not yet available in [region]"
• List available regions

Resources

• Lambda Managed Instances Docs
• Introducing LMI (AWS Blog)
• Build High-Performance Apps with LMI
• Migrating Functions to LMI (AWS Blog)
• LMI Pricing Calculator
• LMI Samples Repository
• AWS Lambda Pricing