docker-swarm-autoscaler VS keda

If you want to have some sort of auto scaling, you will need to monitor to some extent though as this will be the signal for scaling up/down. I noticed that https://github.com/jcwimer/docker-swarm-autoscaler already includes the relevant prometheus configs required for just scaling by cpu.

Nomad, Docker Swarm and other solutions support most of these out of the box, Kubernetes is just the most popular and flexible (with which comes a lot of complexity) solution, it seems.

For example, even something as basic as Docker Swarm will see you a lot of the way through.

> How do you implement healthcheck?

Supported by Docker: https://docs.docker.com/engine/reference/builder/#healthchec...

> Does the loadbalancer know how the healthceck is implemented?

When the health checks pass in accordance with the above config, the container state will change from "starting" to "healthy" and traffic will be able to be routed to it. Until then you can have a web server or whatever show a different page/implement circuit breaking or whatever.

> How do you determine it's time to scale?

Docker Swarm doesn't have an abstraction for autoscaling, though there are a few community projects. One can feasibly even write something like that themselves in an evening: https://github.com/jcwimer/docker-swarm-autoscaler

That said, I mostly ignore this concern because I'm yet to see a workload that needs to dynamically scale in any number of private or government projects that I've worked on. Most of the time people want predictable infrastructure and being able to deal with backpressure (e.g. message queue), though that's different with startups.

> How do you implement always-on-process? service unit, initd, cron?

The service abstraction comes out of the box: https://docs.docker.com/engine/swarm/how-swarm-mode-works/se...

You might also want to decide how to best schedule it: wherever available, on a particular node (hostname/tag/...) or on all nodes, which is actually what Portainer agent does! Example: https://docs.portainer.io/start/install/server/swarm/linux

> How do you export the logs?

Docker supports multiple logging drivers: https://docs.docker.com/config/containers/logging/configure/

> How do you inject configs? /etc/environment, profile.d, systemd config, /etc/bestestapp/config?

Docker and Compose/Swarm support environment variables: https://docs.docker.com/compose/compose-file/#environment

If you need config files, you can also use bind mounts: https://docs.docker.com/storage/bind-mounts/

> What about secrets?

Docker supports secrets out of the box: https://docs.docker.com/engine/swarm/secrets/

> Service discovery? Is unbound/bind9?

Docker Swarm supports built in DNS, even allows for multiple separate networks: https://docs.docker.com/engine/swarm/networking/

> These items are best done in a standard way.

Agreed! Though I'd say that the only two options being "running everything on *nix directly" and "running everything in Kubernetes" is a false narrative! The former can work but can also lead to non-standard and error-prone environments with a horrible waste of human resources, whereas the latter can work but can also lead to overcomplicated and hard to debug environments with a horrible waste of human resources.

The best path for many folk probably lies somewhere in the middle, with Nomad/Swarm/Compose/Docker, regardless of what others might claim. The best path for folks interested in a DevOps career is probably running on cloud managed Kubernetes clusters and just using their APIs to lots of great results, not caring about how expensive that is or how easy it would be to self-host on-prem.

It seems you want something like KEDA (https://keda.sh)

Most just utilize out of the box macro resources available in HPA.

For more advanced use cases there is keda - https://keda.sh/

Thankfully KEDA operator was already part of the cluster, and all Robin had to do was create a ScaledObject manifest targeting the Dispatch ScaleUp event, based on the rabbitmq_global_messages_received_total metric from Prometheus.

Keda

KEDA introduces event-driven scaling to Kubernetes workloads. It integrates with Kubernetes Horizontal Pod Autoscalers and can scale pods based on external metrics from services like databases and message queues (Kafka, RabbitMQ, MongoDB).

# update version 2.8.2 if required kubectl apply -f https://github.com/kedacore/keda/releases/download/v2.8.2/keda-2.8.2.yaml

This is traditionally a AWS Lambda usecase - or an OpenFaas kind of usecase. But very recently i discovered https://keda.sh/ and it seems it is specifically meant for this in a kubernetes environment.

If you deploy the application to Amazon EKS, you can also consider using KEDA to auto-scale your consumer application based on the number of messages in the MSK topic.