AWS Secrets Manager vs SSM Parameter Store: When to Use Each

Introduction

Whenever I am called to review a project and a secret is required - an API key, database credential, or any sensitive value - someone predictably asks:

Should we use AWS Secrets Manager or SSM Parameter Store (SecureString)?

The answer isn't always straightforward (the dreaded, 'It Depends' answer). This post explains the key differences and when to use each service.

SSM Parameter Store

Parameter Store, a tool in AWS Systems Manager, provides secure, hierarchical storage for configuration data management and secrets management - AWS

SSM Parameter Store lets you store configuration data and secrets as key-value pairs. Each parameter has a hierarchical key path (e.g., /service/env/db-password) that helps organize and scope access using IAM.

Value types: Simple string, SecureString (KMS encrypted), Structured data (JSON)

Standard vs Advanced Tiers

Feature	Standard (Free)	Advanced (Paid)
Parameter quota	10,000	100,000
Max value size	4 KB	8 KB
Versioning & Policies	No	Yes

Secrets Manager

AWS Secrets Manager helps you manage, retrieve, and rotate database credentials, application credentials, OAuth tokens, API keys, and other secrets throughout their lifecycles - AWS

AWS Secrets Manager is purpose-built to manage the full lifecycle of secrets.

Key features:

• Managed rotation - Supports AWS database credentials (RDS, Aurora, Redshift, DocumentDB)
• Unmanaged rotation - Write a Lambda function for custom rotation logic
• Cross-region replication
• Versioning
• IaC support
• Max secret size - 64 KB

Feature Comparison

Feature	SSM Parameter Store	Secrets Manager
Cost	Free (Standard) / Low (Advanced)	Higher
Max size	4 KB / 8 KB	64 KB
Encryption	Optional (SecureString)	Always encrypted
Automatic rotation	No	Yes
Cross-region replication	No	Yes
Versioning	Advanced tier only	Yes
IaC support	Limited (exposes SecureString)	Secure
Managed DB credential rotation	No	Yes
Hierarchical organization	Yes	No
Configuration data	Yes	Not intended

When to Use Each

Use SSM Parameter Store When:

• Storing non-sensitive configuration or need free/low-cost parameter storage
• Cross-account or cross-stack sharing of information such as IDs, ARNs, service domains via CDK or CloudFormation
• Storing secrets without requiring rotation or secure IaC support
• You want to avoid the extra cost of Secrets Manager

Use Secrets Manager When:

• Storing credentials, tokens, and API keys needing rotation, versioning, or cross-region support
• You need automatically managed rotation for RDS, Aurora, Redshift, or DocumentDB
• You need custom rotation for other use cases via Lambda
• You require secure IaC usage (CDK or CloudFormation)
• A managed secret lifecycle is worth the cost (regulated/enterprise environments)

Quick Reference Summary

Scenario	Recommendation
Non-sensitive config values	SSM Parameter Store
Cross-stack/account sharing (IDs, ARNs)	SSM Parameter Store
Secrets without rotation needs	SSM Parameter Store (SecureString)
Database credentials with rotation	Secrets Manager
API keys needing rotation	Secrets Manager
Regulated/enterprise environments	Secrets Manager
Cost-sensitive, simple secrets	SSM Parameter Store

Conclusion

Context matters, and your constraints make a difference. Both services have their place:

• SSM Parameter Store excels at hierarchical configuration management with optional encryption, and the free tier makes it ideal for non-sensitive config and cost-conscious teams
• Secrets Manager is the right choice when you need automatic rotation, cross-region replication, or are working in regulated environments where secret lifecycle management is critical