# A routine maintenance takes the application down

Cloud galaxy · Cédric Merlin, CTO · https://merlin-cedric.fr/en/cloud/reboot-404/

After a host maintenance, a private network card changes name and takes the application down: the cause is a chain of five links.

## The problem

After a hosting provider’s maintenance, the application shows “page not found” (404 error) on a whole series of servers.

## The constraint

Everyone suspects the latest database migration. It is not the cause.

## What I did

1. **Too fast.** Clue: the application restarts in 18 seconds instead of 10 minutes. Too fast to be healthy.
2. **A card was renamed.** The private network card changed name on reboot.
3. **Three links fall.** The route to the outside is gone, the secrets vault is unreachable, the application starts without its configuration.
4. **Fixed for good.** I fix each server, then the automation, so the next reboot breaks nothing.

## The result

The cause as a chain of five links, and a written procedure.

Figure: 5 links between the reboot and the error.

## Stack

Linux, Private network, Secrets management, Automation

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Page: https://merlin-cedric.fr/en/cloud/reboot-404/ · Contact: contact@merlin-cedric.fr