haredis

High-availability redis in Node.js

(note: Travis-CI support for this project is a work in progress. If the build badge is red above, it's likely not really a problem with haredis, but rather a problem with Travis-CI running my tests. Tests pass locally for me!)

Idea

haredis is a code wrapper around node_redis which adds fault-taulerance to your application.

Features:

• Drop-in replacement for node_redis
• Easily build a cluster out of 3 or more (default-configured) redis servers
• Auto-failover due to connection drops
• Master conflict resolution (default your servers to master, and haredis will elect the freshest and issue the SLAVEOF commands)
• Freshness judged by an opcounter (incremented on write)
• Locking mechanism to prevent failover contention
• Load-balancing for reads and pub/sub
• One-client pub/sub
• Gossip channel for quick failover

Usage

Start up multiple redis daemons, with no special configuration necessary, and list them like so:

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.
• Run test/basic.js 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.

API differences

createClient

In haredis, createClient works like this:

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 metadata in (such as an opcounter). Defaults to 15.

auth

auth works like this:

function auth({host/port to password object}, callback)

The first argument can be an object of hosts, ports mapped to passwords (i.e., {'1.2.3.1:6379': 'pass1', '1.2.3.3:6379': 'pass2'}), or just the password string.

Load-balancing

haredis can optionally load-balance read operations to random slaves. Pub/sub subscriptions will automatically try to use a slave. For normal read-only commands, you can choose to query a random slave by using the slaveOk() method:

client.slaveOk().GET('foo', function(err, reply) { ...

slaveOk() will only affect the current command.

To load-balance all reads, you can set options.auto_slaveok = true in createClient(). Be advised that this can case problems due to replication delay!

To force a read to go to master when using auto_slaveok, use slaveOk(false) before the command:

client.slaveOk(false).GET('foo', function(err, reply) { ...

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](#1) warning: MASTER is down! (127.0.0.1:6380)
[19:27:58](#1) info: reorientating (node down) in 2000ms
Redis connection gone from end event.
[19:28:00](#1) info: orientating (node down, 2/3 nodes up) ...
[19:28:00](#1) warning: invalid master count: 0
[19:28:00](#1) info: attempting failover!
[19:28:00](#1) info: my failover id: gP0SCM1B
[19:28:00](#1) info: lock was a success!
[19:28:00](#1) info: 127.0.0.1:6381 had highest opcounter (1441) of 2 nodes. congrats!
[19:28:00](#1) info: making 127.0.0.1:6382 into a slave...
[19:28:00](#1) info: 127.0.0.1:6382 is slave
[19:28:00](#1) info: publishing gossip:master for 127.0.0.1:6381
[19:28:00](#1) info: renegotating subSlave away from master
[19:28:00](#1) info: subSlave is now 127.0.0.1:6382
[19:28:00](#1) info: ready, using 127.0.0.1:6381 as master

To get info on which commands are executed on which servers, try setting redis.command_logging = true.

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:

$ make test-cluster

Or in single-mode with a redis server on port 6379:

$ make test

LICENSE - "MIT License"

• Copyright (c) 2012 Carlos Rodriguez, http://s8f.org/
• Copyright (c) 2012 Terra Eclipse, Inc., http://www.terraeclipse.com/

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.