> ## Documentation Index
> Fetch the complete documentation index at: https://docs.sqd.dev/llms.txt
> Use this file to discover all available pages before exploring further.

# Serving GraphQL

> Choose a GraphQL server for your Squid SDK indexer.

It is common (although not required) for squids to serve GraphQL APIs. Historically, the most common way to do that was to [persist the squid data to PostgreSQL](./writing-to-postgres), then attach [OpenReader](#openreader) to it. Although this is still supported, we encourage using [PostGraphile](#postgraphile) or [Hasura](#hasura) in new PostgreSQL-based projects. See [OpenReader's limitations](../reference/openreader/overview#limitations) if you're curious about our motivation.

## PostGraphile

[PostGraphile](https://www.graphile.org/postgraphile/) is an open-source tool that builds powerful, extensible and performant GraphQL APIs from PostgreSQL schemas. Its pros include:

* aggregations;
* reliable support for subscriptions;
* capability for deep API customization;
* organization of API customization code into plugins.

The recommended way of integrating PostGraphile into squid projects is by making a dedicated entry point at `src/api.ts`. A complete example squid implementing this approach is available in [this repository](https://github.com/subsquid-labs/squid-postgraphile-example/).

With this entry point in place, we [create a `sqd` command](https://github.com/subsquid-labs/squid-postgraphile-example/blob/f1fd1691eb59da2c9d57c475a71d0ed44cfed891/commands.json#L58) for running PostGraphile with [`commands.json`](/en/cloud/reference/cli/commands-json), then use it in the [`deploy.api` entry](https://github.com/subsquid-labs/squid-postgraphile-example/blob/f1fd1691eb59da2c9d57c475a71d0ed44cfed891/squid.yaml#L15) of [Squid manifest](/en/cloud/reference/manifest). Although none of this is required, this makes it easier to run the squid both locally (with [`sqd run`](/en/cloud/reference/cli/run)) and in the [Cloud](/en/cloud/overview).

As with other PostGraphile installations, you can extend it with plugins, including your own. Here is an [example plugin for serving the `squidStatus` query](https://github.com/subsquid-labs/squid-postgraphile-example/blob/f1fd1691eb59da2c9d57c475a71d0ed44cfed891/src/api.ts#L11) from the standard Squid SDK GraphQL server schema.

## Hasura

[Hasura](https://hasura.io) is a powerful open-source GraphQL engine. You can use it to:

* expose multiple data sources of different kinds (various databases, APIs etc) via a single API;
* reliably serve subscriptions;
* perform aggregations;
* deeply customize your CRUD API.

You can integrate Hasura with your squid in two ways:

1. **Use Hasura to gather data from multiple sources, including your squid.**

   For this scenario we recommend separating your Hasura instance from your squid, which should consist of just one service (the processor) plus the database. Supply your database credentials to Hasura, then configure it to produce the desired API.

   If you run your squid in our [Cloud](/en/cloud/overview) you can find database credentials in [the app](https://app.subsquid.io/squids).

2. **Run a dedicated Hasura instance for serving the data just from your squid.**

   A complete example implementing this approach is available in [this repository](https://github.com/subsquid-labs/squid-hasura-example). Here's how it works:

   * Locally, Hasura runs in a [Docker container](https://github.com/subsquid-labs/squid-hasura-example/blob/70bb6d703dc90c1bb00b47f3fef7f388ab54e565/docker-compose.yml#L14C1-L28C20). In the Cloud it is managed via the [Hasura addon](/en/cloud/reference/hasura).
   * Hasura metadata is shared among all squid instances by means of the [Hasura configuration tool](../reference/hasura-configuration). The tool can automatically create an initial configuration based on your [TypeORM models](../reference/schema-files/schema-files-codegen#typeorm-codegen), then persist any changes you might make with the web GUI and metadata exports.
   * Admin authentication secret is set via the `HASURA_GRAPHQL_ADMIN_SECRET`. The variable is set in `.env` locally and from a [secret](/en/cloud/resources/env-variables#secrets) in Cloud deployments.

   See the [configuration tool page](../reference/hasura-configuration) and the [repo readme](https://github.com/subsquid-labs/squid-hasura-example#readme) for more details.

## OpenReader

[OpenReader](../reference/openreader/overview) is a GraphQL server developed by the SQD team. Although still supported, it's not recommended for new PostgreSQL-powered projects due to its [limitations](../reference/openreader/overview#limitations), especially for APIs implementing GraphQL subscriptions.

The server uses the [schema file](../reference/schema-files/schema-files-codegen) to produce its [core API](../reference/openreader/api/intro) that can be extended with [custom resolvers](../reference/openreader/configuration/custom-resolvers). Extra features include [DoS protection](../reference/openreader/configuration/dos-protection) and [caching](../reference/openreader/configuration/caching).