Configure HAProxy to Send Write Requests to Leader Node Only

There are a few options regarding implementation of a proxy server to direct writes to a Master node and reads to the Slave nodes in a Neo4j cluster. Commonly, it is recommended to handle this logic in the application code. However, there is another way.

By using the following configuration for HAProxy, you can direct GET requests (reads) to the Slave nodes, while directing everything else (DELETE, POST, PUT) to the Master.

global
daemon
maxconn 256

defaults
mode http
timeout connect 5000ms
timeout client 50000ms
timeout server 50000ms

frontend http-in
bind *:80
acl write_methods method POST DELETE PUT
#Only POST and DELETE methods are used according to the documentation
use_backend neo4j-write if write_methods
default_backend  neo4j-read-only

backend neo4j-read-only
balance roundrobin
option httpchk GET /db/manage/server/causalclustering/read-only
server s1 10.0.1.10:7474 maxconn 32 check
server s2 10.0.1.11:7474 maxconn 32 check
server s3 10.0.1.12:7474 maxconn 32 check

backend neo4j-write
balance roundrobin
option httpchk GET /db/manage/server/causalclustering/writable
server s1 10.0.1.10:7474 maxconn 32 check
server s2 10.0.1.11:7474 maxconn 32 check
server s3 10.0.1.12:7474 maxconn 32 check

The logic here says that by default a request is routed to a follower and if it is a write request (POST, DELETE, PUT), route it to a Master instead.

See the product documentation for more info on this topic: https://neo4j.com/docs/operations-manual/3.5/ha-cluster/haproxy/

The first step in configuring Basic Authentication in HAProxy is to get the base64 representation of username:password.

To do this at the command line, for username neo4j and password neo4j:

$ echo -n "neo4j:neo4j" | base64
bmVvNGo6bmVvYWRtaW4=

Please note that this username-password combination is not valid and only used for demonstration purposes.

Then append HTTP/1.0\r\nAuthorization:\ Basic\ base64_username_password as following:

option httpchk GET /db/manage/server/causalclustering/writable HTTP/1.0\r\nAuthorization:\ Basic\ bmVvNGo6bmVvYWRtaW4=

  • Last Modified: 2020-10-22 22:13:22 UTC by Stefan Armbruster.
  • Relevant for Neo4j Versions: 3.0,3.1,3.2,3.3,3.4,3.5.
  • Relevant keywords cluster, master, writes, load balancer.