Backends Updater (Alpha **)

This demon do following operation in order:

Get list of running containers and identify app containers using specified regex pattern
Generate loadbalancer(nginx) config file with found app containers as backends(upstream servers)
Listen to docker events for any 'start' or 'stop' events.

If any app container is created or stopped, it then add or remove this entry respectively from load balancer configuration, update configuration file and restart nginx . Before updating config file, it takes backup of old configuration file

Installation

Pre-requisite

golang (preferrably ~ 1.3)

Build binary

#Steps to build
git clone project
go build main.go
mv main backendUpdater

Usage

D:\tmp\go\tryOne>main --help
Usage:
  -bkp_dir="": file backup directory(Optional)
  -config="": Configuration file path(*required) eg. /etc/nginx/sites-enabled/default
  -dockerAddr="0.0.0.0:4243": docker bind addresss(Optional)
  -heartbeat=30s: heartbeat interval for containers check. eg 30s , 5m, 30m (Optional)
  -host="127.0.0.1": hostname or IP to attach to containers(optional)
  -service="": Service Pattern to track(*required)
  -since=1412355983: docker events from whence(optional)
  -template="loadbalancer.conf": template file(required)

bkp_dir : Directory to store old config files
dockerAdd : Address to listen for docker remote api
exportfile : Path to export config file (usually sites-enabled folder)
hearteat : Interval to wait before updating file
host : IP Address to attach in backend server list . PORT will be populated from container public port information
service : Regex service pattern to find app containers
since : To track events since XXX
template : load balancer config template

Example

 ./main -dockerAddr http://199.127.219.76:4243  -service "dailyreport[0-9]*.stackexpress.com" -config  "/etc/nginx/sites-enabled/loadbalancer.conf" -heartbeat 30s

System V init script template

A simple template for init scripts that provide the start, stop, restart and status commands.

Getting started

Copy init to /etc/init.d and rename it to something meaningful. Then edit the script and enter that name after Provides: (between ### BEGIN INIT INFO and ### END INIT INFO).

Now set the following three variables in the script:

dir

The working directory of your process.

user

The user that should execute the command.

cmd

The command line to start the process.

Here's an example for an app called backendUpdater

... Provides:     backendUpdater_init     
...

dir="/opt/apps/backendUpdater"
user="root"
cmd='/var/apps/backendUpdater/main -dockerAddr http://127.0.0.1:4243  -service "dailyReport[0-9]*.stackepress.com" -config "default" '

# copy Init script to /etc/init.d/ 
cp init /etc/init.d/backendUpdater_init

Script usage

Start

Starts the app.

/etc/init.d/backendUpdater_init start

Stop

Stops the app.

/etc/init.d/backendUpdater_init stop

Restart

Restarts the app.

/etc/init.d/backendUpdater_init restart

Status

Tells you whether the app is running. Exits with 0 if it is and 1 otherwise.

/etc/init.d/backendUpdater_init status

Logging

By default, standard output goes to /var/log/scriptname.log and error output to /var/log/scriptname.err. If you're not happy with that, change the variables stdout_log and stderr_log.

How code works?

Goals before writing code

Keep update( config file) and restart(nginx ) operation to minimum

i.e If many docker events are triggered in short interval, then update only after populating results from all events. This update interval is customizale with heartbeat command arguments.
- It'll wait for specified heartbeat interval. In this all docker events will be queued. After that each event is processed
- Summary of all queued event is populated into Final Updated Container list
- If app container list is changed, then only loadbalancer config file is updated and nginx restarted, else nothing happened

RoadMap

Backends healthcheck
Remove unhealthy backends

sahilsk/BackendsUpdater