Summary

We have mongodb cluster deployed in internal network where TXT and SRV records are published for second-level domain service-name.tld.

This setup works with mongotools and Compass, however any tool that uses Node.js driver will fail with error message:

Unable to connect: URI must include hostname, domain name, and tld

This is caused by hard-coded check that hostname has 3 parts in src/connection_string.ts#67:

  if (options.srvHost.split('.').length < 3) {
    // TODO(NODE-3484): Replace with MongoConnectionStringError
    throw new MongoAPIError('URI must include hostname, domain name, and tld');
  }

This check is redundant because `dns.promises.resolveTxt` is already capable of handling domain errors with appropriate error codes i.e. `dns.BADNAME`

Thanks!

Motivation

Who is the affected end user?

• Developers using internally managed service discovery tools that use DNS/SRV and have custom host names

How does this affect the end user?

• Developers can't use valid URI to connect to mongodb cluster
• An error is thrown before DNS SRV resolution is attempted

How likely is it that this problem or use case will occur?

• Main path, every MongoClient usage throws this error

If the problem does occur, what are the consequences and how severe are they?

• Unable to connect

Is this issue urgent?

TBD

Is this ticket required by a downstream team?

• No, external request

Is this ticket only for tests?

• No, functional change

Acceptance Criteria

The MongoClient MUST enforce the following:

• If an SRV contains >= 3 '.' separated parts (no change to existing behavior)
  • the returned address MUST end with all parts of the SRV except the leftmost segment
  • i.e. the returned address can only be a child, sibling, or duplicate of the SRV 
  • Example: mongodb+srv://cluster_1.mongodb.com
    • valid return addresses:
      • hosts_2.mongodb.com // sibling
      • hosts_3.cluster_1.mongodb.com // child
      • mongodb.com // duplicate
    • invalid return address: clusters.fakedb.com

• If an SRV contains 1 or 2 dot separated parts
  • the returned address MUST end with all parts of the SRV and have an additional domain level
  • i.e. the returned address can only be child of the SRV
  • Example: `mongodb+srv://mongodb.local`
    • valid return addresses:
      • cluster_1.mongodb.local // child
    • invalid return address:
      • hosts_2.local // sibling
      • mongodb.local // duplicate
• Add new prose tests described in spec

Follow-Up Requirements

• File a ticket for the next major version to require that SRVs with 3+ parts MUST only return addresses that are the child of the SRV.
  • Example: the SRV mongodb.co.uk.org has 3+ parts, but could still return evil.co.uk.org if we allow returned address to be siblings of the SRV