Server-side caching

Apollo Server enables you to define cache control settings (maxAge and scope) for each field in your schema:

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type Post {
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  id: ID!
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  title: String
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  author: Author
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  votes: Int @cacheControl(maxAge: 30)
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  comments: [Comment]
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  readByCurrentUser: Boolean! @cacheControl(maxAge: 10, scope: PRIVATE)
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}

When Apollo Server resolves an operation, it calculates the result's correct cache behavior based on the most restrictive settings among the result's fields. You can then use this calculation to support any form of cache implementation you want, such as by providing it to your CDN via a Cache-Control header.

You can define field-level cache settings statically in your schema definition (as shown above) or dynamically in your resolvers.

Field settings

When caching operation results, it's important to understand:

• Which fields of your schema can be cached safely
• How long a cached value should remain valid
• Whether a cached value is global or user-specific

These details can vary significantly, even among the fields of a single object type. You can specify these details statically in your schema definition or dynamically in your resolvers.

In your schema (static)

Apollo Server defines the @cacheControl directive, which you can use in your schema to define caching behavior either for a single field, or for all fields that return a particular type.

The @cacheControl directive accepts the following arguments:

Use @cacheControl for fields that should always be cached with the same settings. If caching settings might change at runtime, instead use the dynamic method.

Field-level definitions

This example defines cache control settings for two fields of the Post type: votes and readByCurrentUser:

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type Post {
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  id: ID!
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  title: String
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  author: Author
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  votes: Int @cacheControl(maxAge: 30)
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  comments: [Comment]
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  readByCurrentUser: Boolean! @cacheControl(maxAge: 10, scope: PRIVATE)
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}

In this example:

• The value of a Post's votes field is cached for a maximum of 30 seconds.
• The value of a Post's readByCurrentUser field is cached for a maximum of 10 seconds, and its visibility is restricted to a single user.

Type-level definitions

This example defines cache control settings for all schema fields that return a Post object:

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type Post @cacheControl(maxAge: 240) {
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  id: Int!
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  title: String
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  author: Author
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  votes: Int
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  comments: [Comment]
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  readByCurrentUser: Boolean!
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}

If another object type in this schema includes a field of type Post (or a list of Posts), that field's value is cached for a maximum of 240 seconds:

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type Comment {
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  post: Post! # Cached for up to 240 seconds
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  body: String!
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}

Note that field-level settings override type-level settings. In the following case, Comment.post is cached for a maximum of 120 seconds, not 240 seconds:

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type Comment {
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  post: Post! @cacheControl(maxAge: 120)
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  body: String!
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}

In your resolvers (dynamic)

You can decide how to cache a particular field's result while you're resolving it. To support this, Apollo Server provides a cacheControl object in the info parameter that's passed to every resolver.

The cacheControl object includes a setCacheHint method, which you call like so:

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const resolvers = {
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  Query: {
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    post: (_, { id }, _, info) => {
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      info.cacheControl.setCacheHint({ maxAge: 60, scope: 'PRIVATE' });
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      return find(posts, { id });
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    }
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  }
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}

The setCacheHint method accepts an object with the same fields as the @cacheControl directive.

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import 'apollo-cache-control';

Default maxAge

By default, the following schema fields have a maxAge of 0 (meaning their values are not cached unless you specify otherwise):

• All root fields (i.e., the fields of the Query and Mutation objects)
• Fields that return an object or interface type

Scalar fields inherit their default cache behavior (including maxAge) from their parent object type. This enables you to define cache behavior for most scalars at the type level, while overriding that behavior in individual cases at the field level.

As a result of these defaults, no schema fields are cached by default.

Setting the default maxAge

You can set a default maxAge (instead of 0) that's applied to every field that doesn't specify a different value.

Set your default maxAge in the ApolloServer constructor, like so:

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const server = new ApolloServer({
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  // ...other options...
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  cacheControl: {
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    defaultMaxAge: 5, // 5 seconds
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  },
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}));

Caching with a CDN

Whenever Apollo Server sends an operation response that has a non-zero maxAge, it includes a Cache-Control HTTP header that describes the response's cache policy.

The header has this format:

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Cache-Control: max-age=60, private

If you run Apollo Server behind a CDN or another caching proxy, you can configure it to use this header's value to cache responses appropriately. See your CDN's documentation for details (for example, here's the documentation for Amazon CloudFront).

Using GET requests

Because CDNs and caching proxies only cache GET requests (not POST requests, which Apollo Client sends for all operations by default), we recommend enabling automatic persisted queries and the useGETForHashedQueries option in Apollo Client.

Alternatively, you can set the useGETForQueries option of HttpLink in your ApolloClient instance, but this is less secure because your query string and GraphQL variables are sent as plaintext URL query parameters.

Disabling Cache-Control

You can prevent Apollo Server from setting Cache-Control headers by setting calculateHttpHeaders to false in the ApolloServer constructor:

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const server = new ApolloServer({
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  // ...other options...
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  cacheControl: {
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    calculateHttpHeaders: false,
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  },
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}));

Caching with responseCachePlugin (advanced)

You can cache Apollo Server query responses in stores like Redis, Memcached, or Apollo Server's in-memory cache.

In-memory cache setup

To set up your in-memory response cache, you first import the responseCachePlugin and provide it to the ApolloServer constructor:

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import responseCachePlugin from 'apollo-server-plugin-response-cache';
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const server = new ApolloServer({
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  // ...other options...
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  plugins: [responseCachePlugin()],
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});

On initialization, this plugin automatically begins caching responses according to field settings.

The plugin uses the same in-memory LRU cache as Apollo Server's other features. For environments with multiple server instances, you might instead want to use a shared cache backend, such as Memcached or Redis.

Memcached/Redis setup

See Using Memcached/Redis as a cache storage backend.

Identifying users for PRIVATE responses

If a cached response has a PRIVATE scope, its value is accessible by only a single user. To enforce this restriction, the cache needs to know how to identify that user.

To enable this identification, you provide a sessionId function to your responseCachePlugin, like so:

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import responseCachePlugin from 'apollo-server-plugin-response-cache';
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const server = new ApolloServer({
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  // ...other settings...
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  plugins: [responseCachePlugin({
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    sessionId: (requestContext) => (requestContext.request.http.headers.get('sessionid') || null),
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  })],
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});

The cache uses the return value of this function to identify the user who can later access the cached PRIVATE response. In the example above, the function uses a sessionid header from the original operation request.

If a client later executes the exact same query and has the same identifier, Apollo Server returns the PRIVATE cached response if it's still available.

Separating responses for logged-in and logged-out users

By default, PUBLIC cached responses are accessible by all users. However, if you define a sessionId function (as shown above), Apollo Server caches up to two versions of each PUBLIC response:

• One version for users with a null sessionId
• One version for users with a non-null sessionId

This enables you to cache different responses for logged-in and logged-out users. For example, you might want your page header to display different menu items depending on a user's logged-in status.

Configuring reads and writes

In addition to the sessionId function, you can provide the following functions to your responseCachePlugin to configure cache reads and writes. Each of these functions takes a GraphQLRequestContext (representing the incoming operation) as a parameter.