Focused, hands-on DevOps and server-side problems with hints, feedback, and automated solution checks.
On a dual-homed Linux server, a service bound to one network's IP address may still be reachable from another network. Learn how to prevent this unexpected access without disrupting legitimate connections.
On a dual-homed Linux server, a service bound to the IP address of one interface may still accept connections that arrive through the other interface. Learn how to reach such a service through an interface it doesn't listen on, using a routing trick.
A distroless container serves a debug interface on its own loopback address. Can you reach this debug endpoint using nothing but standard Docker commands?
Practice using SHA-256 checksums to verify file integrity, detect corrupted or modified files, and confirm that downloaded data matches the original.
Practice authenticating to an HTTP API from the command line using both a username and password and a bearer token, and learn a couple of tricks along the way.
Practice one of the most common command-line combinations for HTTP API access: fetch a JSON response with curl and pipe it into jq to pretty print, reshape, or get only the relevant parts.
Practice calling HTTP APIs from the command line: send JSON bodies with POST, PUT, and PATCH, upload a file, delete a resource, and read the status codes the server answers with.
Learn the basics of accessing HTTP APIs from the command line: call different endpoints, read the response body, headers, and status code, follow redirects, and request an alternative representation of a server resource.
An internal service started receiving requests from unexpected IP addresses. Identify the unexpected sources and find out which systems are behind them.
Practice manually resolving public domains, internal hostnames, and locally defined names to the corresponding IP addresses so you feel confident next time a DNS issue occurs.
