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HAProxy Installation

Document guides through the installation and configuration of the HAProxy service which is required to route ClickHouse request to MongoDB’s current master instance.


VM Requirements

  • Separate VM
  • RAM: 1 GB
  • Storage: 10 GB


  1. Install version 1.8.8,
  2. Make it accessible by IP address from the networks where ClickHouse instances located. Also configure firewall to allow access to a proxy port 27017 of this VM


Change /etc/haproxy/haproxy.cfg contents to contain:

listen mongodb_cluster
 bind [vm_ip]:[vm_port]
 log local0
 option tcp-check
 # MongoDB Wire Protocol
 tcp-check send-binary 3a000000 # Message Length (58)
 tcp-check send-binary EEEEEEEE # Request ID (random value)
 tcp-check send-binary 00000000 # Response To (nothing)
 tcp-check send-binary d4070000 # OpCode (Query)
 tcp-check send-binary 00000000 # Query Flags
 tcp-check send-binary 61646d696e2e # fullCollectionName (admin.$cmd)
 tcp-check send-binary 24636d6400 # continued
 tcp-check send-binary 00000000 # NumToSkip
 tcp-check send-binary FFFFFFFF # NumToReturn
 # Start of Document
 tcp-check send-binary 13000000 # Document Length (19)
 tcp-check send-binary 10 # Type (Int32)
 tcp-check send-binary 69736d617374657200 # ismaster:
 tcp-check send-binary 01000000 # Value : 1
 tcp-check send-binary 00 # Term

tcp-check expect binary 69736d61737465720001 #ismaster True

option tcpka
 option tcplog
 log global
 server mongo-node-01 [mongodb_ip_1]:[mongodb_port_1] check inter 2000
 server mongo-node-02 [mongodb_ip_2]:[mongodb_port_1] check inter 2000
 server mongo-node-03 [mongodb_ip_3]:[mongodb_port_1] check inter 2000

Here are suggestions for the dummy values:

  • [vm_ip] (e.g. - HAProxy VM IP address to listen on
  • [vm_port] (e.g. 27017) - HAProxy VM port to listen ClickHouse requests on [mongodb_ip_1]/[mongodb_ip_2]/[mongodb_ip_3] (e.g.,, - IP addresses of MongoDB instances.
  • [mongodb_port_1]/[mongodb_port_2]/[mongodb_port_3] (e.g.27017`) - Ports of MongoDB instances respectively If you have more than 3 MongoDB replicas, add them too.