High-availability redis in Node.js
npm install haredisharedis
-------
High-availability redis in Node.js
Idea
====
haredis is a code wrapper around node_redis
which adds fault-taulerance to your application. Start up multiple redis daemons,
with no special configuration necessary, and list them like so:
``javascript`
var redis = require('haredis')
, nodes = ['1.2.3.1:6379', '1.2.3.2:6379', '1.2.3.3:6379']
, client = redis.createClient(nodes)
;
...then use client as you would use node_redis.
If the master node goes down, haredis will automatically determine which node
to promote to master, and keep standby connections to the others.
If multiple haredis clients are connected, a locking mechanism is implemented
to prevent contention between failover attempts.
To see this in action,
- Set up 3 local redis daemons on ports 6380-82
- 6380 should be SLAVEOF NO ONE. 6381 and 82 should be slaves to 6380.test/basic.js
- Run or test/pubsub.js (try multiple to test contention)
- Kill the process listening on 6380 (master). haredis will auto-failover to
the node it detects is freshest, set that to master, and the others to slaves!
- Bring up 6380, and it will be added as standby for failover.
Difference: createClient
========================
In haredis, createClient works like this:
`javascript`
function createClient([host/port array], options)
The first argument can be an array of hosts (using default port), ports (using
localhost), or colon-separated strings (i.e., 1.2.3.4:6379). haredis will
attempt to connect to all of these servers.
options corresponds to the same options you would pass
node_redis. haredis
additionally supports:
- haredis_db_num {Number} database number that haredis should store metadata15
in (such as an opcounter). Defaults to .
One-client pub/sub
==================
In redis, pub/sub is a "mode" which excludes the use of regular commands while
subscriptions are active. Normally you need to make separate client objects to
use publish on one and subscribe on the other.
haredis adds the nice ability to use pub/sub simultaneously with regular
commands. This is because it keeps internal redis clients in pub/sub mode for
internal "gossip", but also makes it available for users. Of course this is
optional, and you can always maintain a separate haredis client for subscribes
if you wish.
Advice
======
For proper failover, a majority of the nodes need to be still online. This means
that the minimum number of nodes should be 3. Under the minimum setup, you can
lose up to 1 node. If only 1/3 are up, commands will be queued indefinitely until
another node comes up.
Debugging/verbose logging
=========================
To see what's under the hood, try setting redis.debug_mode = true, and you can
see the failover process in detail:
`
19:27:58 info: set on 127.0.0.1:6380 (master default)
19:27:58 warning: MASTER is down! (127.0.0.1:6380)
19:27:58 info: reorientating (node down) in 2000ms
Redis connection gone from end event.
19:28:00 info: orientating (node down, 2/3 nodes up) ...
19:28:00 warning: invalid master count: 0
19:28:00 info: attempting failover!
19:28:00 info: my failover id: gP0SCM1B
19:28:00 info: lock was a success!
19:28:00 info: 127.0.0.1:6381 had highest opcounter (1441) of 2 nodes. congrats!
19:28:00 info: making 127.0.0.1:6382 into a slave...
19:28:00 info: 127.0.0.1:6382 is slave
19:28:00 info: publishing gossip:master for 127.0.0.1:6381
19:28:00 info: renegotating subSlave away from master
19:28:00 info: subSlave is now 127.0.0.1:6382
19:28:00 info: ready, using 127.0.0.1:6381 as master
19:28:00 info: set on 127.0.0.1:6381 (master default)
Running tests
=============
haredis includes the test suite from node_redis
which can be run in single or clustered mode.
If you have redis daemons running locally on ports 6380, 6381 and 8382, you can
run the clustered test with:
`bash`
$ make test-clustered
Or in single-mode with a redis server on port 6379:
`bash``
$ make test
LICENSE - "MIT License"
=======================
Copyright (c) 2012 Carlos Rodriguez, http://s8f.org/
Copyright (c) 2012 Terra Eclipse, Inc., http://www.terraeclipse.com/
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