Helpers alongside the main container.
WHAT AN INIT CONTAINER IS
One that runs to completion before the main container starts.
WHAT IT SUITS
Waiting for a dependency Preparing files or permissions Fetching configuration
WHAT HAPPENS IF IT FAILS
The pod retries, and the main container never starts.
WHAT A SIDECAR IS
A container running alongside the main one, for its lifetime.
WHAT IT SUITS
Log shipping Proxying network traffic Refreshing credentials Exporting metrics
WHAT THEY SHARE
The network address, and any shared volumes.
WHY THAT MATTERS
The sidecar reaches the main container on the loopback address.
WHAT TO BE CAREFUL WITH
Sidecars that do not exit, preventing jobs from completing Ordering, since containers start together by default Resource consumption, which adds to every pod
WHAT THAT LAST POINT MEANS
A sidecar on a hundred pods is a hundred copies.
WHAT TO WEIGH
Whether the function belongs in the application instead.
WHAT TO PREFER
Fewer containers per pod, unless the coupling is genuine.
WHAT MAKES COUPLING GENUINE
Needing the same network namespace or filesystem.
WHAT TO AVOID
Sidecars added by habit rather than need.
