This override is used by the cache adapter (opens in a new tab) that is provided by OpenNext to the NextServer. It is also used by OpenNext if enableCacheInterception is set to true in the configuration.

It is used for retrieving and updating the ISR/SSG cache as well as the fetch cache used by Next.js. It does not handle anything related to cache tags (i.e. revalidateTag and revalidatePath)

If you want to better understand how to implement your own IncrementalCache, the easiest way would be to take a look at the existing included IncrementalCache (opens in a new tab).

One thing to note is that it is not used at build time, only at runtime. This means that you'll have to upload the cache yourself if you want to use the prebuilt routes/pages (And this is mandatory for ISR/SSG routes with fallback:false). All the cache files are present in the .open-next/cache folder. The one under BUILD_ID are for the ISR/SSG cache and the one under __fetch/BUILD_ID are for the fetch cache.

Included IncrementalCache

s3

The S3 IncrementalCache will store fetch and ISR/SSG cache in an S3 bucket. It is used by default if you don't provide any IncrementalCache in your configuration. It uses the @aws-sdk/client-s3 to interact with S3.

Requirements

• You need to provide the CACHE_BUCKET_REGION, CACHE_BUCKET_KEY_PREFIX, CACHE_BUCKET_NAME environment variables to your server.

s3-lite

The S3Lite IncrementalCache will store fetch and ISR/SSG cache in an S3 bucket This implementation is a lighter version of the s3 IncrementalCache as it uses aws4fetch to interact with S3.

Requirements

• You need to provide the CACHE_BUCKET_REGION, CACHE_BUCKET_KEY_PREFIX, CACHE_BUCKET_NAME, AWS_ACCESS_KEY_ID, AWS_SECRET_ACCESS_KEY and AWS_SESSION_TOKEN environment variables to your server.

dummy

The Dummy IncrementalCache is a dummy implementation that throws exceptions for every method. It should not be used unless you want to disable the cache.

fs-dev

The FsDev IncrementalCache is a simple implementation that stores the cache in the .open-next/cache folder and interact with it using the filesystem. It is useful for development purposes only.

Requirements

It needs to run on the local filesystem, and expect to be run from the OpenNext output.

multi-tier-ddb-s3

The MultiTierDdbS3 IncrementalCache is a more complex implementation. Cache are stored in a local In Memory LRU cache as well as in S3. DynamoDB is used to keep local cache in sync between multiple instances of the server. It uses aws4fetch to interact with S3 and DynamoDB.

How does it work

On get :

1. When a cache is requested, it first checks the local cache. If the cache is not found, it will fetch it from S3 and store it in the local cache.
2. If the local cache exist for this key, it will check metadata in DynamoDB to see if the cache is still valid. If it is not, it will fetch the cache from S3 and store it in the local cache.
3. If the local cache is valid, it will return it.

On update :

1. When a cache is updated, it will first try to update the cache in S3.
2. If the update is successful, it will update the metadata in DynamoDB.
3. Finally, it will update the local cache.

Requirements

• You need to provide the CACHE_BUCKET_REGION, CACHE_BUCKET_KEY_PREFIX, CACHE_BUCKET_NAME, CACHE_DYNAMO_TABLE, AWS_ACCESS_KEY_ID, AWS_SECRET_ACCESS_KEY and AWS_SESSION_TOKEN, OPEN_NEXT_LOCAL_CACHE_TTL_MS (optional), OPEN_NEXT_LOCAL_CACHE_SIZE(optional) environment variables to your server.
• DynamoDB table should have a primary key path of type String and a sort key tag of type String. (It can reuse the same table as the one used by the default tagCache)