SSM Parameter Store

Quick summary: Free, hierarchical config/secret store. No auto-rotation. Best for application configuration and lower-sensitivity secrets.

See also: Secrets Manager vs SSM Parameter Store for a detailed comparison.

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🔰 What Is Parameter Store?

Parameter Store is a centralized, hierarchical configuration management service. Think of it as a key-value store organized in folders — like a filesystem for configuration.

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Parameter Types & Tiers

Types

Type	Encryption	Use Case	Example
String	None	URLs, feature flags, config	jdbc:mysql://db.example.com:3306/mydb
StringList	None	Comma-separated values	us-east-1,eu-west-1,ap-southeast-1
SecureString	KMS encrypted	Passwords, API keys	SuperSecret123!

Tiers

Feature	Standard	Advanced
Max size	4 KB	8 KB
Max parameters	10,000	100,000
Parameter policies	❌	✅ (expiration, notification)
Throughput	40 TPS (default)	Up to 10,000 TPS
Cost	Free	$0.05/month per parameter
Higher throughput	Extra charge	Included

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Hierarchical Organization

/                              (root)
├── prod/
│   ├── myapp/
│   │   ├── db-url             String
│   │   ├── db-password        SecureString (KMS encrypted)
│   │   ├── db-port            String
│   │   ├── feature-flags      StringList
│   │   └── api-key            SecureString
│   └── shared/
│       ├── cors-origins       StringList
│       └── jwt-secret         SecureString
├── staging/
│   └── myapp/
│       ├── db-url             String
│       └── db-password        SecureString
└── dev/
    └── myapp/
        ├── db-url             String
        └── db-password        SecureString

Benefits of Hierarchy

• GetParametersByPath — load all config for an environment in one call
• IAM scoping — restrict access by path prefix
• Environment isolation — same parameter names, different paths

// IAM policy: Allow dev team access only to /dev/ parameters
{
  "Effect": "Allow",
  "Action": ["ssm:GetParameter*"],
  "Resource": "arn:aws:ssm:us-east-1:123456789012:parameter/dev/*"
}

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Java SDK Integration

Lambda — Load Config at Init Time

public class OrderHandler implements RequestHandler<APIGatewayProxyRequestEvent, APIGatewayProxyResponseEvent> {
    
    private static final SsmClient SSM = SsmClient.create();
    private static final Map<String, String> CONFIG;
    
    // Load ALL config at init time (runs once per cold start)
    static {
        GetParametersByPathResponse response = SSM.getParametersByPath(
            GetParametersByPathRequest.builder()
                .path("/prod/myapp/")
                .withDecryption(true)
                .recursive(true)
                .build());
        
        CONFIG = response.parameters().stream()
            .collect(Collectors.toMap(
                p -> p.name().substring(p.name().lastIndexOf('/') + 1),  // Extract param name
                Parameter::value));
    }
    
    public APIGatewayProxyResponseEvent handleRequest(APIGatewayProxyRequestEvent event, Context context) {
        String dbUrl = CONFIG.get("db-url");
        String apiKey = CONFIG.get("api-key");
        // Use cached config — no SSM calls on warm invocations
    }
}

ECS Task Definition

{
  "containerDefinitions": [{
    "name": "myapp",
    "secrets": [
      {
        "name": "DB_PASSWORD",
        "valueFrom": "arn:aws:ssm:us-east-1:123:parameter/prod/myapp/db-password"
      },
      {
        "name": "API_KEY",
        "valueFrom": "arn:aws:ssm:us-east-1:123:parameter/prod/myapp/api-key"
      }
    ]
  }]
}

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CloudFormation Integration

# Method 1: Parameter section (String/StringList only, NOT SecureString)
Parameters:
  DbUrl:
    Type: AWS::SSM::Parameter::Value<String>
    Default: /prod/myapp/db-url

# Method 2: Dynamic references (works with ALL types including SecureString)
Resources:
  MyRdsInstance:
    Type: AWS::RDS::DBInstance
    Properties:
      Engine: mysql
      # String parameter
      DBName: "{{resolve:ssm:/prod/myapp/db-name}}"
      # SecureString parameter (MUST use ssm-secure)
      MasterUserPassword: "{{resolve:ssm-secure:/prod/myapp/db-password:1}}"
      # Secrets Manager
      # MasterUserPassword: "{{resolve:secretsmanager:prod/db-secret:SecretString:password}}"

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Parameter Policies (Advanced Tier)

// Expiration: Delete parameter after date
{
  "Type": "Expiration",
  "Version": "1.0",
  "Attributes": { "Timestamp": "2025-12-31T00:00:00.000Z" }
}

// Notification before expiration
{
  "Type": "ExpirationNotification",
  "Version": "1.0",
  "Attributes": { "Before": "15", "Unit": "Days" }
}

// Alert if not updated for N days
{
  "Type": "NoChangeNotification",
  "Version": "1.0",
  "Attributes": { "After": "90", "Unit": "Days" }
}

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SecureString & KMS

Reading a SecureString requires TWO permissions:

{
  "Effect": "Allow",
  "Action": [
    "ssm:GetParameter",       // Permission to read the parameter
    "kms:Decrypt"             // Permission to decrypt with the KMS key
  ],
  "Resource": [
    "arn:aws:ssm:us-east-1:123:parameter/prod/myapp/*",
    "arn:aws:kms:us-east-1:123:key/my-key-id"
  ]
}

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Parameter Store vs Environment Variables

Feature	SSM Parameter Store	Lambda Env Variables
Max size	4-8 KB per param	4 KB total
Encryption	KMS (SecureString)	KMS (optional)
Centralized	✅ Shared across functions	❌ Per-function
Versioning	✅	❌
Hierarchy	✅	❌
Dynamic updates	✅ (next cold start)	❌ (redeploy required)
Cost	Free (Standard)	Free

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🎯 DVA-C02 Exam Tips

SSM Parameter Store Exam Cheat Sheet

1. Free for Standard tier (up to 10,000 parameters)
2. SecureString needs BOTH ssm:GetParameter AND kms:Decrypt permissions
3. CloudFormation SecureString = MUST use {{resolve:ssm-secure:...}}
4. GetParametersByPath = load all config under a path prefix in one call
5. No auto-rotation — use custom Lambda or Secrets Manager instead
6. Advanced tier = parameter policies (expiration, notification)
7. ECS secrets can reference SSM parameters directly
8. Hierarchy enables IAM path-based access control

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🧪 Practice Questions

Q1. CloudFormation template needs SecureString from SSM. How?

A) AWS::SSM::Parameter::Value<SecureString>
B) {{resolve:ssm-secure:/path/to/param}}
C) Direct string in template
D) Custom resource

✅ Answer & Explanation

B — SecureString in CloudFormation requires dynamic references with ssm-secure. The Parameters section doesn't support SecureString type.

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Q2. App needs auto-rotating DB password. Which service?

A) Secrets Manager
B) SSM Parameter Store
C) KMS
D) IAM

✅ Answer & Explanation

A — Secrets Manager has native auto-rotation for RDS. SSM Parameter Store has no built-in rotation.

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Q3. Lambda reads SecureString but gets AccessDeniedException. Role has ssm:GetParameter. What's missing?

A) ssm:DescribeParameters
B) kms:Decrypt on the KMS key
C) ssm:GetParameters
D) VPC endpoint

✅ Answer & Explanation

B — SecureString is encrypted with KMS. The role needs both ssm:GetParameter AND kms:Decrypt.

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🔗 Resources

• SSM Parameter Store Guide
• CloudFormation Dynamic References
• Parameter Store vs Secrets Manager