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The Caravan of Services: Composing Containerized Applications
One wagon may travel alone, but a kingdom moves as a caravan. Beyond the Castle Gate: From Containers to Applications Packing a workshop into a container solves an important problem, but it does not solve the entire journey. In the previous chapter of The Kingdom in the Clouds, we explored how containers package an application together with the runtime, libraries, and dependencies it needs to operate consistently. That gives engineers a portable unit that can travel from a development machine to a test environment and eventually into production with far fewer surprises. Yet most modern applications are not single workshops sealed inside single wagons. They are collections of services, databases,…
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Packing the Castle: Understanding Containers
A well-packed workshop should work the same no matter where the road carries it. There is a particular kind of software failure that becomes almost funny after you have encountered it enough times. An application works perfectly on one developer’s machine, refuses to cooperate on another, behaves differently in testing, and then develops an entirely new personality after deployment. The code is the same, the database is supposedly the same, and everyone involved is reasonably certain that the necessary dependencies were installed. Yet somewhere between one machine and another, the application crossed an invisible border and discovered that the laws of physics had changed. For years, software teams fought these…
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The Kingdom in the Clouds: When Software Leaves the Castle
The strongest kingdoms are not bound to a single castle, but built to endure wherever their people must go. For much of software history, we built applications as though we were building castles. The walls gave us boundaries. We knew where the application lived, where its data lived, and which machines carried the work. Even complicated systems offered a comforting sense of geography because their important pieces occupied places engineers could identify and understand. When something failed, there was usually a server, process, database, or network connection somewhere that could be examined. Modern software has been steadily dismantling that certainty. Applications move between environments, workloads appear and disappear, and infrastructure…
