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  1. Compass
  2. COMPASS-6208

Investigate changes in PM-2290: Make dedicated config servers optional for sharded clusters

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    • Icon: Investigation Investigation
    • Resolution: Done
    • Icon: Major - P3 Major - P3
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    Description

      Original Downstream Change Summary

      The design document has more details about the changes which is being reviewed in WRITING-8015.

      User-Facing Syntax Changes
      Users will need to modify the change management scripts if they wish to opt-in into new mode
      Users will need to make the startup script roll forward/back compatible
      Users will need to write the script performing the roll forward/back procedure

      API Changes
      The internal SDAM protocol is likely to change. Will write SDAM tests, no spec changes required (do we have a document for internal SDAM extensions?).
      We will avoid adding a new API version

      Config File Changes
      The new “catalogShard” option is added to the "sharding.clusterRole" section of the config file, “--catalogShard” command line option is added to the mongod.

      Description of Linked Ticket

      +underlined text+

      Epic Summary

      Summary

      We will make dedicated config servers optional for sharded clusters. Customers will have the option to designate a special shard that will hold both user data and config data. For one-shard clusters on Atlas, the shard will automatically be a special shard with both the shard role and config role.

      Motivation

      Eliminating dedicated config servers will reduce both the cost and the architectural complexity involved in single-shard sharded clusters. On Atlas, a single-shard M30 sharded cluster costs TWICE as much as an M30 replica set. This project would bring cost parity to single-shard clusters on Atlas and will make it easier for customers to start out with a sharded cluster or switch to a sharded cluster.

      It also supports other use-cases:

      • Serverless v2 - Serverless would like to remove the cost and complexity of dealing with config servers.
      • Kubernetes - Some customers prefer to use a sharded cluster with a single shard because the mongos can act as a proxy. No config server would mean better resource utilization and less operational overhead

      Cast of Characters

      Documentation

      Product Description
      Scope Document
      Technical Design Document

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            backlog-server-pm Backlog - Core Eng Program Management Team
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