Tag Archives: load balancer

networking, server

Configuring NGINX Load Balancer Reverse Proxy

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Below is example of NGINX reverse proxy with 2 backend load balanced:

upstream backend {
  ip_hash;
  server localhost:8080 fail_timeout=3;
  server localhost:8081 fail_timeout=3;
}

server {
  listen 80;
  server_name mydomain.com;

  location / {
    proxy_pass http://backend/;
    proxy_redirect default;
    proxy_cookie_domain localhost mydomain.com;
  }
}
  • The upstream directive defines a cluster named backend of 2 backend servers (localhost:8080 and localhost:8081). fail_timeout parameter specifies request to the node will be deemed fail if no response is obtained after 3 seconds.
  • The ip_hash directive causes request coming from same ip to be associated with the same backend. This is often called sticky session. Other popular strategy is using cookie.
  • The cluster name backend is referenced by proxy_pass directive inside location

Add down parameter to avoid request being passed to specific backend:

upstream backend {
  ip_hash;
  server localhost:8080 fail_timeout=3;
  server localhost:8081 fail_timeout=3 down;
}

This is handy when performing no-outage release.

Don’t forget to reload the configuration using nginx -s reload

Read Related NGINX Docos

networking

Reverse Proxy and Load Balancing using Apache mod_proxy

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Reverse Proxy is a type of proxy server that retrieves the resource on behalf of the client such that the response appears to come from the reverse proxy server itself. One useful application of reverse proxy is when you want to expose a server on your internal network to the internet.

Load Balancing is a technique of distributing requests into several backend servers, hence providing redundancy and scalability. Many Java EE app servers came built-in with clustering feature allowing session to be replicated across all nodes in the cluster.

Apache has few modules that can be used to setup the two above. Following is a guide on how to set it up.

  1. Ensure you have an apache-httpd installed. This guide is written against httpd 2.4. If you’re on OSX most likely you’ve already got httpd installed.
  2. Figure out where is your httpd.conf file located. Typically it’s at $HTTPD_ROOT/conf/httpd.conf.
  3. Enable following modules. Module can be enabled by uncommenting (removing the ‘#’ character at the beginning) the LoadModule directive on your httpd.conf:
    [sourcecode]
    LoadModule proxy_module modules/mod_proxy.so
    LoadModule proxy_http_module modules/mod_proxy_http.so
    LoadModule proxy_balancer_module modules/mod_proxy_balancer.so
    LoadModule slotmem_shm_module modules/mod_slotmem_shm.so
    LoadModule lbmethod_byrequests_module modules/mod_lbmethod_byrequests.so
    [/sourcecode]
  4. (Optional) depending on your operating system setup, you might need to change the user & group httpd will use to start the process. On my OSX I have to change it into my own user / group (or root). Use the User and Group directive for this
    [sourcecode]
    User gerrytan
    Group staff
    [/sourcecode]
  5. Add the following proxy / load balancer configuration
    [sourcecode]

    BalancerMember http://192.168.1.101:8080 route=node1
    BalancerMember http://192.168.1.102:8080 route=node2
    ProxySet stickysession=BALANCEID

    ProxyPassMatch ^(/.*)$ balancer://mycluster$1
    ProxyPassReverse / http://192.168.1.101:8080/
    ProxyPassReverse / http://192.168.1.102:8080/
    ProxyPassReverseCookieDomain 192.168.1.101 localhost
    ProxyPassReverseCookieDomain 192.168.1.102 localhost
    [/sourcecode]

    The  directive specifies we are defining a load balancer with a name balancer://mycluster with two backend servers (each specified by the BalancerMember directive). In my case my backend servers are 192.168.1.101:8080 and 192.168.1.102:8080. You can add additional IPs to your network interface to simulate multiple backend servers running in different hosts. Note the existence of the route attribute which will be explained shortly.

    The ProxySet directive is used to set the stickysession attribute specifying a cookie name that will cause request to be forwarded to the same member. In this case I used BALANCEID, and in my webapp I wrote a code that will set the cookie value to balancer.node1 or balancer.node2 respectively. When apache detects the existence of this cookie, it will only redirect request to BalancerMemeber which route attribute matches the string after the dot (in this case either node1 or node2). Thanks to this blog article for explaining the step: http://www.markround.com/archives/33-Apache-mod_proxy-balancing-with-PHP-sticky-sessions.html.

    The ProxyPassMatch directive is used to capture and proxy the requests that came into the apache httpd server (the proxy server). It takes a regular expression to match the request path. For example, assuming I installed my httpd on localhost:80, and I made a request to http://localhost/foo, then this directive will (internally) forward the request to http://192.168.1.101:8080/foo.

    The ProxyPassReverse directive is used to rewrite http redirect (302) sent by the backend server, so the client does not bypass the reverse proxy.

    ProxyPassReverseCookieDomain is similar to ProxyPassReverse but applied to cookies.

Few words of warning

There are plenty methods of configuring reverse proxy, this guide uses http reverse proxy which might not deliver the best performance. You might also want to consider AJP reverse proxy for better performance.