Currently my position is that code replacement in a containerized environment is a “square peg in a round hole” kind of situation. Code replacement has its use cases where a typical cut-over is just not feasible, be it on telephone switches before containers, upgrading a drone in mid-flight or upgrading high availability IoT devices.
In any case certain modules/processes have to be written with an awareness that code replacement is a possibility in order for the upgrade to be successful which tends to increase the complexity at the lowest level. So while the VM has the basic capability for code replacement, it isn’t a capability that can be taken advantage of “for free” on the system level - it adds yet another concern that winds through the entire codebase.
With containers you have the opportunity to address that complexity explicitly through architecture. Daniel Azuma describes one approach taken in tanx that uses Horde supervisors.
