* apollo-server: add health check with async callback for backend querying
* apollo-server: add changelog entry
* change to engine healthcheck url, add disable, 503 on fail and conform to rfc
* apollo-server: fixed health check comment grammar and location
* update changelog to include new endpoint
Apollo Persisted Queries is a standard for sending queries as short hashes
instead of full strings, designed to work well with GET requests. It is
implemented by servers including the Apollo Engine Proxy, and by the
apollo-link-persisted-query client.
A common configuration is to set up persisted queries on production servers but
not in development. It is still convenient to leave apollo-link-persisted-query
always on, though. While apollo-link-persisted-query can detect that servers
don't support PQs, it works better if the server actually says it doesn't
support the PQ, instead of trying to process a request without a query and
potentially printing a confusing stack trace. This commit makes apollo-server
directly return PersistedQueryNotSupported instead of allowing confusing stack
traces to occur.
The express-graphql reference implementation [provides a check]
(2e27a73358/src/index.js (L201-L208))
to protect against cases where a GET request is made that does not
have a `query` parameter where the GraphQL query would be present.
Without this guard, graphql-js's `parse` will return `undefined`
for the `DocumentNode` since it has no document to read. Subsequently
passing this to `isQueryOperation` results in a `TypeError`, because
we are providing `undefined` where `getOperationAst` [expects to get
a DocumentNode](5fe39262a3/src/utilities/getOperationAST.js (L19)).
A new test file is added for `runHttpQuery`, as one previously did
not seem to exist.
