Focused, hands-on DevOps and server-side problems with hints, feedback, and automated solution checks.
A container port published on a server's internal IP is still reachable from the external network. Learn how to restrict access with firewall rules without disrupting legitimate connections.
Learn how to access a service bound to localhost of the Docker host from a bridge-networked container, without exposing the service to the local network or disabling network isolation.
Learn how to access services running on the Docker host from a bridge-networked container, without hardcoding host IP addresses or disabling network isolation.
Play a security researcher: identify the hosts a black-box container keeps making encrypted HTTPS calls to, route them through a MITM proxy, fake the certificate, and see what the container sends over the network.
Sometimes you need an app to talk to a different backend, but its configuration is unknown or the destination address is hard-coded. Practice overriding hostname resolution for a single Docker container to redirect its requests without modifying the app or rebuilding its image.
A distroless container serves a debug interface on its own loopback address. Can you reach this debug endpoint using nothing but standard Docker commands?
You are containerizing the dev workflows of a legacy Python service and you need to find out which external services its test suite talks to. Can you think of an easy way to do it?
Ad-hoc containers are a handy way to run command-line tools without installing them on the host. Use one to access a production Redis server and turn off a feature flag. But beware of the gotcha: the production server can only be tunneled to the localhost.
Explore the container networks of a freshly installed Docker host: find the default network, its subnet and gateway, and the Linux interface behind it.
Can you get several builds of an app running side by side without port conflicts, so you can test them simultaneously?
