Docker has radically changed the way admins roll out their software in many companies. However, regular updates are still needed. How does this work most effectively with containers?
From an admin’s point of view, Docker containers have much to recommend them: They can be operated with reduced permissions and thus provide a barrier between a service and the underlying operating system. They are easy to handle and easy to replace. They save work when it comes to maintaining the system on which they run: Software vendors provide finished containers that are ready to run immediately. If you want to roll out new software, you download the corresponding container and start it – all done. Long installation and configuration steps with RPM, dpkg, Ansible, and other tools are no longer necessary. All in all, containers offer noticeable added value from the sys admin’s perspective.
…No matter what the reasons for updating applications running in Docker containers, as with normal systems, you need a working strategy for the update. Because running software in Docker differs fundamentally from operations without a container layer, the way updates are handled also differs.
Several options are available with containers, which I present in this article, but first, you must understand the structure of Docker containers, so you can make the right decisions when updating.
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