Load balancing

Here we’ll cover the case where pavics-sdi is installed on more than one machine and you want to balance the load across these machines. This is done with NGINX and requires modifications to docker-compose.yml and creating a configuration file for the NGINX server.

Modifying the docker-compose.yml

To enable load balancing, we need a proxy to redirect requests to machines according to their usage. This is done by mapping proxy ports (5XXXX) to the service ports, such as those of flyingpigeon (8093) and malleefowl (8091).

docker-compose.yml

proxy:
  image: nginx
  ports:
    - "58094:8094"
    - "58093:8093"
    - "58091:8091"
  volumes:
    - ./config/proxy/conf.d:/etc/nginx/conf.d
    - ./config/proxy/nginx.conf:/etc/nginx/nginx.conf
  restart: always

Modifying the Nginx configuration

In the config/proxy directory, there should be a file named nginx.conf. This file can be edited for example to specify the number of worker_processes. In the conf.d directory, there are a number of additional configuration file for each load balanced service, for example flyingpigeon.conf, which would look like:

config/proxy/conf.d/flyingpigeon.conf

upstream flyingpigeon {
    hash $http_machineid;
    server <server1 url>:8093;
    server <server2 url>:8093;
    server <server3 url>:8093;
}
server {
    listen 8093;
    location / {
        proxy_pass http://flyingpigeon;
    }
}

This tell the proxy, listing on port 8093, to redirect requests to servers 1, 2 or 3 according to the machineid argument passed in the request header. That is, requests with the same machineid will be sent to the same server. This is important to control since output files are not automatically visible to all servers. So if for example process A downloads a file from a remote server and process B subsets the file, both have to be run on the same machine otherwise process B won’t find the downloaded file.

Note

• Server configuration is static
• It is not possible to assign port numbers to environment variables (eg $PORT_NUMBER)
• When you change a configuration file and restart NGINX to pick up the new configuration, it implements a graceful restart. Both the old and new copies of NGINX run side-by-side for a short period of time. The old processes don’t accept any new connections and terminate once all their existing connections terminate.