CODEWITHSUNDEEP
linuxkerneldocker
bhartsb
bhartsb

Reputation: 1366

How does Docker allow portable containers if the Kernel libraries change

If my program depends on some function of a kernel library, and that function in turn has a chain of dependencies, how does docker stay small and portable without taking a snapshot of all the kernel libraries (and managing dependency issues at a function rather than library level)? In other words how does it insulate itself from changes in Kernel libraries from one version to the next, and does it do so at a library or function granlarity?

Also what if my application has a software stack where for example one function is compatible with a future version of kernel library A whereas a second function that uses kernel library A is no longer compatible. In other words:

function 1&2 both depend on and work with functions in kernel Lib A version 1.0

function 1 works with Lib A version 1.1 function 2 breaks with Lib A version 1.1 (function 2 still needs Lib A version 1.0)

I don't know much about Docker so this is a newbie question.

Upvotes: 15

Views: 3893

Answers (1)

user149341
user149341

Reputation:

There is no such thing as a "kernel library". The closest things to what you're describing are:

  • libc, which is part of the container image, and hence does not change.

  • The Linux kernel ABI, which is mostly constant. While some changes are occasionally made to the kernel ABI, this is done as rarely as possible - kernel developers do everything possible to maintain backwards compatibility. Where changes are made, it is most often in components that would not be relevant to applications running in a container (e.g, audio / video output, dynamic device management, etc).

Upvotes: 19

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