# AmazonLinuxImageSsmParameterBaseProps

Base properties for an Amazon Linux SSM Parameter.

Extends: AmazonLinuxImageSsmParameterBaseProps
Extends: AmazonLinuxImageSsmParameterBaseOptions
Used as props by: AmazonLinuxImageSsmParameterBase

- Source: [`aws-ec2/lib/machine-image/common.ts`](https://github.com/aws/aws-cdk/blob/v2.274.0/packages/aws-cdk-lib/aws-ec2/lib/machine-image/common.ts#L67)
- Type last changed: v2.76.0 · 20 Apr 2023

## Example

```ts
// The code below shows an example of how to instantiate this type.
// The values are placeholders you should change.
import { aws_ec2 as ec2 } from 'aws-cdk-lib';

declare const userData: ec2.UserData;
const amazonLinuxImageSsmParameterBaseProps: ec2.AmazonLinuxImageSsmParameterBaseProps = {
  parameterName: 'parameterName',

  // the properties below are optional
  additionalCacheKey: 'additionalCacheKey',
  cachedInContext: false,
  userData: userData,
};
```

## Properties

- `additionalCacheKey`: string — Adds an additional discriminator to the `cdk.context.json` cache key.

  **Default:** no additional cache key

- `cachedInContext`: boolean = false — Whether the AMI ID is cached to be stable between deployments.

  By default, the newest image is used on each deployment. This will cause
  instances to be replaced whenever a new version is released, and may cause
  downtime if there aren't enough running instances in the AutoScalingGroup
  to reschedule the tasks on.

  If set to true, the AMI ID will be cached in `cdk.context.json` and the
  same value will be used on future runs. Your instances will not be replaced
  but your AMI version will grow old over time. To refresh the AMI lookup,
  you will have to evict the value from the cache using the `cdk context`
  command. See https://docs.aws.amazon.com/cdk/latest/guide/context.html for
  more information.

  Can not be set to `true` in environment-agnostic stacks.

- `parameterName`: string (required) — The name of the SSM parameter that contains the AMI value.

- `userData`: [UserData](/cdk/api/v2/docs/aws-cdk-lib.aws_ec2.UserData.html) — Initial user data.

  **Default:** Empty UserData for Linux machines