26.7. REST endpoint for HA status information

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26.7.1. Introduction
26.7.2. The endpoints
26.7.3. Examples

26.7.1. Introduction

A common use case for Neo4j HA clusters is to direct all write requests to the master instance while using slaves for read operations. This allows for maximum write performance, while distributing the read load. This way you get read scalability and failover for your deployment. The most common way to achieve this is to place a load balancer in front of the HA cluster, an example being shown with HA Proxy. As you can see in that guide, it makes use of a REST endpoint to discover which instance is the master and direct write load to it. In this section, we’ll deal with this REST endpoint and explain its semantics.

26.7.2. The endpoints

Each HA instance comes with 2 endpoints regarding its HA status. They are complimentary but each may be used depending on your load balancing needs and your production setup. Those are:

/db/manage/server/ha/master
/db/manage/server/ha/slave

To use them, just do an HTTP GET at either and you’ll get back the following:

HA REST endpoint responses

Endpoint	Instance State	Returned Code	Body text
`/db/manage/server/ha/master`	Master	`200 OK`	`true`
`/db/manage/server/ha/master`	Slave	`404 Not Found`	`false`
`/db/manage/server/ha/slave`	Master	`404 Not Found`	`false`
`/db/manage/server/ha/slave`	Slave	`200 OK`	`true`

26.7.3. Examples

From the command line, a common way to ask those endpoints is to use curl. With no arguments, curl will do an HTTP GET on the URI provided and will output the body text, if any. If you also want to get the response code, just add the -v flag for verbose output. Here are some examples:

Requesting master endpoint on a running master with verbose output

#> curl -v localhost:7474/db/manage/server/ha/master
* About to connect() to localhost port 7474 (#0)
*   Trying ::1...
* connected
* Connected to localhost (::1) port 7474 (#0)
> GET /db/manage/server/ha/master HTTP/1.1
> User-Agent: curl/7.24.0 (x86_64-apple-darwin12.0) libcurl/7.24.0 OpenSSL/0.9.8r zlib/1.2.5
> Host: localhost:7474
> Accept: */*
>
< HTTP/1.1 200 OK
< Content-Type: text/plain
< Access-Control-Allow-Origin: *
< Transfer-Encoding: chunked
< Server: Jetty(6.1.25)
<
* Connection #0 to host localhost left intact
true* Closing connection #0

Requesting slave endpoint on a running master without verbose output:

#> curl localhost:7474/db/manage/server/ha/slave
false

Finally, requesting the master endpoint on a slave with verbose output

#> curl -v localhost:7475/db/manage/server/ha/master
* About to connect() to localhost port 7475 (#0)
*   Trying ::1...
* connected
* Connected to localhost (::1) port 7475 (#0)
> GET /db/manage/server/ha/master HTTP/1.1
> User-Agent: curl/7.24.0 (x86_64-apple-darwin12.0) libcurl/7.24.0 OpenSSL/0.9.8r zlib/1.2.5
> Host: localhost:7475
> Accept: */*
>
< HTTP/1.1 404 Not Found
< Content-Type: text/plain
< Access-Control-Allow-Origin: *
< Transfer-Encoding: chunked
< Server: Jetty(6.1.25)
<
* Connection #0 to host localhost left intact
false* Closing connection #0