parse

#!/bin/bash

################################################################
################################################################
## Luis Elizondo <lelizondo@gmail.com>
## Apache License 2.0
##
## This file will parse the Environment variables created by
## node containers linked to the varnish container
## and automatically create a default.vcl configuration file
## 
## The configuration file will create a load balancer and add
## each of the node containers linked.
##
## Varnish is not configured to use the reverse proxy features
## that it has, it just a load balancer.
##
################################################################
################################################################

# Get the Environment variables and save them in the variable envs
envs=`printenv`

# Remove the default.vcl file
rm /etc/varnish/default.vcl

# Loop through all of our variables
for env in $envs
do
  # separate the name of the variable from the value
  IFS== read name value <<< "$env"  
  
  # if the variable has PORT_3000_TCP_ADDR it means this is a
  # variable created by a node container linked to the varnish
  # container
  if [[ $name == *PORT_3000_TCP_ADDR* ]]; then

# create a backend for each node container found in the variables
cat >> /etc/varnish/default.vcl << EOF
  backend ${name} {
    .host = "${value}";
    .port = "3000";
  }
  
EOF

  fi
done

# once we have all the containers ready, we create the
# load balancer, since we're gonna loop again, we just
# create the first line
cat >> /etc/varnish/default.vcl << EOF

  director lb round-robin {
  
EOF

# loop again to add each backend created
for env in $envs
do
  IFS== read name value <<< "$env"  
  if [[ $name == *PORT_3000_TCP_ADDR* ]]; then

# create each backend in the load balancer
cat >> /etc/varnish/default.vcl << EOF
    { .backend = ${name}; }
EOF

  fi
done

# close the load balancer line
# and add the balancer as the req.backend
cat >> /etc/varnish/default.vcl << EOF

  }
  
  sub vcl_recv {
    set req.backend = lb;
  }
EOF