How HAProxy Balances Mongo Reads

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Azita Abdollahi edited this page May 6, 2025 · 1 revision

How HAProxy Balances Mongo Reads

HAProxy forwards client connections to secondary MongoDB members using round-robin balancing.

Setup Summary

frontend mongodb_reads listens on port 27018
backend mongodb_secondaries includes mongodb2 and mongodb3
mode tcp means no protocol inspection (needed for MongoDB)

This allows:

Efficient distribution of read queries
HAProxy health checks to ensure only live secondaries are used

You must ensure:

Reads are allowed on secondaries (rs.secondaryOk())
Clients use readPreference: secondaryPreferred or similar