socket. IO build distributed web push server

socket.io It is more popular at present web Real-time push frame , It is based on nodejs Language development , The underlying use engine.io Realization . With the help of nodejs The asynchronous nature of language , It has achieved good performance . But for a single instance socket.io The carrying capacity is still limited , It can only accommodate at most 3000 individual long-polling Way of client connection .

take socket.io Conduct Distributed There are two difficulties in expansion ：

1. When load balancing, the connection must always be connected to a node

If the client uses long-polling Connect by long rotation training , Then each rotation training will produce a new request , If there is no restriction . It is possible to connect to colony New in socket.io Node , Cause an exception to occur .

resolvent ： Use nginx Of ip_hash Realization session sticky , Let the client always connect to colony On the inner node .

2. Message push between multiple instances

When colony A node in wants to connect to colony When all clients of send messages , When some clients are load balanced ip_hash May be assigned to other nodes , At this time, you need to publish push messages to other nodes , Let other nodes push to the client at the same time .

resolvent ： Use redis The publish and subscribe function of is similar to socket.io-redis Open source library , Realize message push between nodes .

Ready to install software ：

nginx, nodejs, redis And one. socket.io application , Like a chat The server , See the official website here for an example .

Specific steps ：

1. take socket.io The application is deployed into two instances , For example, assign different port numbers to each instance on the same host 4000, 5000：

http.listen(4000, function(){   console.log('listening on *:4000'); });

2. To configure nginx file , Set up load balancing proxy

upstream chat_nodes {         ip_hash;         server 127.0.0.1:4000;         server 127.0.0.1:5000; }

And reverse proxy settings （ Note that in order to support websocket agreement , Need to nginx To upgrade to 1.3.12 Above version

location / {         proxy_pass              http://chat_nodes;         proxy_set_header        Upgrade $http_upgrade;         proxy_set_header        Connection "upgrade";         proxy_http_version      1.1;         proxy_set_header        Host $host;         proxy_set_header        X-Real-IP $remote_addr;         proxy_set_header        X-Forwarded-For $proxy_add_x_forwarded_for;     }

After configuration , restart nginx.

3. install nodejs modular socket.io-redis

sudo npm install socket.io-redis

4. In the original socket.io Initialization in the application io Join at io Of redis Adapter ：

var redis = require('socket.io-redis'); io.adapter(redis({ host: 'localhost', port: 6379 }));

5. Restart each socket.io application , To test .

Other considerations ：

because nginx Reverse proxy mechanism and socket.io Automatic reconnection mechanism , The above architecture also has high availability , That is, when a node down operation period , Clients previously connected to this node will automatically reconnect to other nodes .

The number of nodes can be increased or decreased at any time , There is no need to suspend service , Only need to modify nginx The configuration can be .

nginx Of ip_hash Is based on ip Calculated in the first three paragraphs of , in other words ip Only D Two clients with different segments must be connected to the same The server On , You should pay attention to this when testing .

Can pass redis Subscription and publishing services to achieve the same with other systems colony Communication for , Complete the management of the cluster .