Cesar Chew at 17:25, 24 November 2014

2014-11-24T17:25:05Z

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{{Cat|Nginx}}

<slideshow style="nobleprog" headingmark="⌘" incmark="…" scaled="true" font="Trebuchet MS" >
;title: Load balancing with nginx
;author: Bernard Szlachta (NobleProg Ltd)
</slideshow>

=== nginx as load balancer ⌘===
* A common usage pattern - one or more nginx servers, serving static content directly, and sending dynamic requests onto a cluster of Java servers
* Helps provide good uptime and improved performance

=== Load balancing algorithms ⌘===
* Round-robin (default)
:* Connection 1 to host 1, connection 2 to host 2, connection 3 to host 1 etc etc
* ip_hash
:* Provides consistent mapping between client and upstream server
* least connections
:* Sends each connection to the backend with the fewest connections
:* Use with care
=== Simple load balancing example ⌘===
;
upstream app {
server app1.example.com:8080;
server app2.example.com:8080;
server app3.example.com:8080;
}

server {
location / {
proxy_pass http://app;
}
}

=== Backend health ⌘===
* We can disable a backend if we are unable to connect to it:

upstream app {
server app1.example.com:8080 max_fails=3 fail_timeout=30s;
server app2.example.com:8080 max_fails=3 fail_timeout=30s;
server app3.example.com:8080 max_fails=3 fail_timeout=30s;
}

* This stops trying to use a backend after connection attempts have ailed three times in a row
* Will try using it again after 30 seconds
=== 'Sticky' backends ⌘===
* Want each client to be served by the same backend?
* Use ip_hash
* Only looks at the first three octets of the IP
:* Therefore often unsuitable for internal-facing applications

=== 'Sticky' backends example ⌘===
;
upstream app {
ip_hash;
server app1.example.com:8080 max_fails=3 fail_timeout=30s;
server app2.example.com:8080 max_fails=3 fail_timeout=30s;
server app3.example.com:8080 max_fails=3 fail_timeout=30s;
}

=== Least connections ⌘===
* Good in theory
* Can lead to 'interesting' problems with servers constantly being added/removed
:* Server overloaded, starts to fail connections
:* Removed from pool, number of connections falls
:* Now healthy again and has no connections, so suddenly flooded with connections
:* Server overloaded, starts to fail connections...

=== Least connections example ⌘===
;
upstream app {
least_conn;
server app1.example.com:8080 max_fails=3 fail_timeout=30s;
server app2.example.com:8080 max_fails=3 fail_timeout=30s;
server app3.example.com:8080 max_fails=3 fail_timeout=30s;
}

=== Keepalive connections ⌘===
* Keep a connection 'pool' to the backends and recycles them
* Lower overhead for each individual request as no need to create a new TCP connection
* If more connections are required than the pool size, these will be dynamically created as before

=== Keepalive example ⌘===
;
upstream app {
ip_hash;
keepalive 32;
server app1.example.com:8080 max_fails=3 fail_timeout=30s;
server app2.example.com:8080 max_fails=3 fail_timeout=30s;
server app3.example.com:8080 max_fails=3 fail_timeout=30s;
}

=== Weights ⌘===
* Sometimes you may be balancing across backends of varying power
* Use weights to signify which servers should get more or less connections
* Higher weight - more connections

=== Weight example ⌘===
;
upstream backend {
ip_hash;
server backend1.example.com weight=2;
server backend2.example.com;
server backend3.example.com;
server backend4.example.com;
}

=== Node maintenance ⌘===
* A node can be temporarily disabled in the config, for example when upgrades are to be carried out on it
;
upstream backend {
ip_hash;
server backend1.example.com down;
server backend2.example.com;
server backend3.example.com;
server backend4.example.com;
}

=== Exercise ⌘===
* Download the HTTP daemons:

[[File:Httpservers.tar.gz]]

* Run each of them in separate windows
* Create round-robin load balancer setup with backends at 127.0.0.1:8001 and 127.0.0.1:8002
* Stop the daemon on 8002. What happens?
* Change the config so that connections to the 8002 daemon automatically cease when it has failed

Load balancing with nginx - Revision history

Cesar Chew at 17:25, 24 November 2014