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Networking was HARD until I Learned these 20 Concepts
20 Networking Concepts Every Developer Should Understand
I still remember the afternoon I spent three hours debugging why my Spring Boot service couldn’t connect to a PostgreSQL container. The application worked perfectly when I ran it locally. The database was running. The credentials were correct. But the moment I moved everything into Docker Compose, I got connection refused errors that made no sense.
I checked the logs. I checked the configuration. I even restarted everything twice, which is the developer equivalent of turning it off and on again.
The problem? I was using localhost in my JDBC URL. Inside the container, localhost meant the container itself, not my host machine. The database was running on a completely different network namespace. I had been writing code for years without truly understanding what happens when one machine tries to talk to another.
That day taught me something important: you can build entire applications without understanding networking, until you can’t. And when you can’t, the confusion hits hard because networking concepts are invisible. There’s no stack trace for a misconfigured subnet mask. No compiler warning for a firewall rule blocking port 5432.
