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For ordinary, mostly static application settings, start with AWS Systems Manager Parameter Store. Use AWS Secrets Manager for credentials and other secrets that need rotation, cross-account access, or fine-grained audit logging. Choose AWS AppConfig when configuration must change safely at runtime, such as feature flags and operational toggles.

Which AWS service fits your configuration?

The services overlap in storing configuration values, but they are built for different change and security needs. AWS describes Parameter Store as a general-purpose parameter store, Secrets Manager as a service for managing secrets, and AppConfig as a way to deploy dynamic configuration safely.

Need Best starting point Why it fits Typical values
Static key-value settings without deployment validation Parameter Store Hierarchical names, IAM controls, versions, KMS-backed SecureString values, and integrations with AWS services. Environment names, endpoint URLs, resource identifiers, approved AMI IDs, and tuning parameters.
Frequently changed settings or safer configuration deployment AppConfig Validation, gradual rollout, rollback based on CloudWatch alarms, and local caching through the AppConfig Agent. Feature flags, operational toggles, tunable parameters, and allow/deny lists.
Credentials and other secrets Secrets Manager Purpose-built secret rotation, cross-account access, and fine-grained audit logging. Database credentials, API keys, OAuth tokens, private keys, and certificates.

These are starting points, not rigid data-type rules. For example, an encrypted setting that does not need secret-lifecycle features may fit Parameter Store SecureString; credentials that require rotation are a better fit for Secrets Manager.

Use Parameter Store for ordinary application parameters

Parameter Store is a practical home for values that an application or deployment process needs to look up centrally but that do not need a dedicated dynamic rollout workflow. Parameters can be retrieved by name or organized into paths, and AWS services including Lambda, ECS/Fargate, CloudFormation, CodeBuild, and AppConfig can integrate with the store.

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Organize names around ownership and environment

Use a consistent hierarchy that identifies the application and environment, with additional segments where they help define ownership or purpose. For example, /myapp/prod/database/host and /myapp/dev/log-level make the setting’s scope legible and support path-based retrieval and IAM policy design. Avoid placing unrelated applications or environments under a path that must share the same permissions.

Choose the right parameter type

  • String: A single value, such as a service endpoint or a log level.
  • StringList: A comma-separated list of values.
  • SecureString: A value encrypted with AWS Key Management Service (KMS).

SecureString encrypts the parameter value, not its name, description, or other metadata. Do not put sensitive information in String or StringList parameters. AWS security guidance recommends SecureString to encrypt and protect secret data, but encryption alone does not provide the rotation and lifecycle features that may make Secrets Manager the better choice for credentials.

Know the tier and size limits

AWS publishes the following limits per account and Region for Parameter Store. Standard parameters have no additional Parameter Store charge; advanced parameters add parameter policies and cross-account sharing and incur charges.

Parameter Store tier Maximum parameters per account and Region Maximum value size Notable tier features
Standard 10,000 4 KB No additional Parameter Store charges.
Advanced 100,000 8 KB Parameter policies and cross-account sharing; charges apply.

Parameter Store retains the 100 most recent versions of each parameter. If a configuration document exceeds the applicable value limit, do not work around it by scattering fragments among unrelated parameter names; select a store and retrieval design that can handle the document as a coherent, versioned configuration.

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Use Secrets Manager when secret lifecycle matters

Secrets Manager is the stronger boundary for database passwords, API keys, OAuth tokens, private keys, and certificates when they need automatic rotation, cross-account access, or fine-grained audit logging. Those needs are more important than whether a value could technically fit in a SecureString parameter.

Parameter Store SecureString remains appropriate for encrypted configuration that does not need those purpose-built lifecycle capabilities. When using a customer-managed KMS key, align both IAM permissions and the KMS key policy so only intended principals can decrypt. AWS notes that users allowed to retrieve parameters encrypted with the AWS-managed key may be able to view all such SecureString content in the account; use access boundaries that match the sensitivity and ownership of the values.

Use AppConfig for configuration that changes at runtime

AppConfig is designed for settings whose changes should be validated and released with control rather than read once during deployment. It supports pre-deployment validation, gradual rollout, automatic rollback when a configured CloudWatch alarm fires, and local caching with the AppConfig Agent. These features make it a better fit than a plain parameter lookup for feature flags, operational switches, and tunable values that may change while an application is running.

Changing an ECS task parameter does not update a running task

When ECS or Fargate resolves a Parameter Store value into an environment variable, it resolves that value when the task starts. Updating the parameter does not change the environment of an already-running task. To apply the new value through environment-variable injection, start replacement tasks or force a new deployment. If the application must read updated configuration without replacing tasks, use a runtime retrieval approach such as the AppConfig Agent rather than relying on startup-time environment variables.

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Match the configuration store to document size

Parameter Store is intended for small values. AWS AppConfig quota documentation lists a 2 MB default and 4 MB maximum for its hosted configuration store, and a 2 MB limit enforced by AppConfig for an S3-backed configuration profile. Secrets Manager supports values up to 64 KB.

Store or profile Document or value size Qualification
Parameter Store standard 4 KB Maximum parameter value.
Parameter Store advanced 8 KB Maximum parameter value.
AppConfig hosted configuration store 2 MB default; 4 MB maximum AppConfig quota documentation.
AppConfig S3-backed profile 2 MB Maximum enforced by AppConfig.
Secrets Manager 64 KB Maximum secret value.

For larger structured configuration, evaluate an AppConfig-supported store or another AWS data service against access patterns, consistency needs, validation, and operational ownership. The size limit alone does not determine the right choice.

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Plan access, retrieval, and change handling

  1. Classify the value. Decide whether it is ordinary configuration, encrypted configuration, a secret, or a setting that must change dynamically.
  2. Choose a store based on both sensitivity and update behavior. Use the service comparison above; do not treat encryption as a substitute for rotation or rollout controls.
  3. Define a path convention. Include application and environment, and add ownership or purpose segments where those distinctions support access boundaries.
  4. Grant least-privilege access. Scope IAM permissions to the required paths and actions. For SecureString values using a customer-managed KMS key, also grant the intended principals the necessary KMS permissions and ensure the key policy permits the intended access.
  5. Decide when consumers read values. Establish whether each consumer reads once at startup, caches locally, or needs runtime refresh. This is especially important for ECS/Fargate environment-variable injection.
  6. Plan for retrieval scale. Review API throughput settings and quotas before broad or high-scale retrieval; AWS advises evaluating throughput early to avoid throttling.
  7. Choose change controls that match risk. Use Parameter Store versions and change notifications where appropriate; use AppConfig validation, gradual deployment, and alarm-based rollback when configuration changes need controlled release.

For any store, keep sensitive values out of names and descriptions, and ensure the application’s retrieval permissions match the intended environment boundary. Treat configuration deployment as part of application operations: a stored value is useful only if consumers can read the right version at the right time.

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