mreithub/do-failover repository overview

⁠do-failover - automatic failover for HTTP(S) based services on DigitalOcean

do-failover helps you switch between a main and hot-standby server on [DigitalOcean][do] (using their Floating IP feature).

⁠Environment

• API_KEY: Your digitalocean.com API key
• FAILOVER_MODE: 'main' or 'standby' (or disabled if not set)
• FLOATING_IP: the IP that's been shared by the main and standby server
• FAILOVER_CHECK: local URL(s) to check to determine the health of this server (split by '|')
• FAILOVER_MAIN: URL(s) of the main server (if we're on the standby server) (URLs are split by '|')
• FAILOVER_MAIN_HOST (optional): Set the 'Host' header for requests to FAILOVER_MAIN URLs (allows to ignore DNS while still checking the validity of SSL certs)

⁠Operation

There are two modes: main and standby:

⁠main:

When in main mode, the failover script will try to acquire/keep the Floating IP (as long as all of the URLs in FAILOVER_CHECK can be successfully fetched).

It runs as follows (once a minute):

• Request all the URLs in FAILOVER_CHECK. If one or more of the checks don't succeed -> fail
• Check if we have the floating IP in question. If we do -> success
• Try to acquire the floating IP.

⁠standby:

When in standby mode, the script will only take control of the floating IP if the main server is deemed unhealthy (i.e. at least one of the URLs in FAILOVER_MAIN return with an error code)

It does the following (once a minute):

• Checks all the URLs in FAILOVER_CHECK (i.e. the health of the local service(s)). If one or more of the checks didn't succeed -> fail
• Checks if it controls the floating IP. If it does -> success
• Check the URLs in FAILOVER_MAIN (to see if the main server is healthy). If it is -> success
• Try to acquire the floating IP.