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Even with containerized workloads, you still have an ingress, or SPOF (or multiple, when using multicast), and the seamless restart is meant for exactly those p

Even with containerized workloads, you still have an ingress, or SPOF (or multiple, when using multicast), and the seamless restart is meant for exactly those processes. Nginx is often used (https://kubernetes.github.io/ingress-nginx/ https://kubernetes.github.io/ingress-nginx/), or when you use AWS, GCS etc they provide such a service for you. Not sure how the cloud providers do it though, maybe combination of low DNS TTL and rolling restart since they often have huge fleets of servers which handle ingress?

nullify88 5y ago
A container though should be immutable and ideally shouldn't have changes made to it. If the container were to die, it'd revert back to the old version? It looks to me like these seamless upgrades would be an anti pattern to containers. With ingress you'd have a load balancer in front or have it routed in the network layer using BGP.
- wereHamster 5y ago
  How do you restart the load balancer though, without dropping traffic?
  - cbb330 5y ago
    two nginx load balancers, reroute to the secondary via dns, restart primary
  - nullify88 5y ago
    You would need more than one to do a rolling restart. Alternatively to do it with one instance of a software load balancer is a bit more work, spin another instance up and update DNS. Wait for traffic to the old one to die as TTLs expire, then decommission. But I agree it isn't as easy as a in place upgrade.
  - deadbunny 5y ago
    2 LBs and a VIP/DNS switch.
- krab 5y ago
  I think the parent was talking more about the fact that at some point, you have a component that should be available as much as possible. In the case you mention, that would be the load balancer. Being able to upgrade it in place might be easier than other ways.
Grollicus 5y ago
If you really want to have no SPOF you'd probably build something like this: Multihomed IP <-> Loadbalancer <-> Application By having the same setup running on multiple locations you can replace the load banacers by taking one location offline (stop announcing the corresponding route). Application instances can be replaced by taking the application instance out of the load balancer.
xyzzy_plugh 5y ago
> Not sure how the cloud providers do it though At least some I am familiar with operate at the packet level and can hand off live "connections" to a peer or hot standby, along with full session state. Remember that with TCP or anything else, the abstract session is an illusion.

nullify88 5y ago

A container though should be immutable and ideally shouldn't have changes made to it. If the container were to die, it'd revert back to the old version? It looks to me like these seamless upgrades would be an anti pattern to containers. With ingress you'd have a load balancer in front or have it routed in the network layer using BGP.

wereHamster 5y ago
How do you restart the load balancer though, without dropping traffic?
- cbb330 5y ago
  two nginx load balancers, reroute to the secondary via dns, restart primary
- nullify88 5y ago
  You would need more than one to do a rolling restart. Alternatively to do it with one instance of a software load balancer is a bit more work, spin another instance up and update DNS. Wait for traffic to the old one to die as TTLs expire, then decommission. But I agree it isn't as easy as a in place upgrade.
- deadbunny 5y ago
  2 LBs and a VIP/DNS switch.
krab 5y ago
I think the parent was talking more about the fact that at some point, you have a component that should be available as much as possible. In the case you mention, that would be the load balancer. Being able to upgrade it in place might be easier than other ways.

Grollicus 5y ago

If you really want to have no SPOF you'd probably build something like this: Multihomed IP <-> Loadbalancer <-> Application By having the same setup running on multiple locations you can replace the load banacers by taking one location offline (stop announcing the corresponding route). Application instances can be replaced by taking the application instance out of the load balancer.

xyzzy_plugh 5y ago

> Not sure how the cloud providers do it though At least some I am familiar with operate at the packet level and can hand off live "connections" to a peer or hot standby, along with full session state. Remember that with TCP or anything else, the abstract session is an illusion.