Add odo watch + quarkus:dev live reload support as one mode of the S2I

[emmanuelbernard]

In Quarkus, we have an integrated live reload model that listens to resources (like config files) and .class changes.
When someone hits refresh in the browser, Quarkus checks if any file has changed and restart the app
(not the JVM).
It’s fast enough (less than .5 to 1s for a reasonable size app).
So for Quarkus we do need of odo watch to rsync specific directories so that Quarkus’s live reload that we call quarkus:dev today kicks in accordingly.

Note that it's different from a classical S2I Java process which AFAIK is like this:

1. push code
2. s2i starts maven build
3. start java app off the maven build

In the Live reload mode, the model is more like this

1. enable odo watch
2. deploy the container which will run mvn package quarkus:dev and be ready to listen to requests
3. on .class or resource changes in a specific set of directories, rsync said files into the container in the specific location /some/determined/path/target
4. on resource changes, Quarkus does its magic from within the container

[cescoffier]

Isn't odo tied to OpenShift. What about something working with "bare" Kubernetes too?

[geoand]

Currently odo is tied to Openshift yes

[emmanuelbernard]

I don't know if there is an accepted watch model in Kubernetes atm. CC @kadel

[kadel]

I don't know if there is an accepted watch model in Kubernetes atm. CC @kadel

@emmanuelbernard
There is skaffold. It can watch over files similar to what odo is doing, but last time I checked it was rebuilding the image every time and there was no way to do hot reload.

Isn't odo tied to OpenShift. What about something working with "bare" Kubernetes too?

@cescoffier
Right now it is OpenShift only. But we have plans to add "bare" Kubernetes support, it is on our roadmap.

[emmanuelbernard]

Thanks kadel, anyways let's see what we can do for odo first.

[geoand]

I can take up the work on the odo side - provided that we figure out what builder image should be used @kadel

[gsmet]

@emmanuelbernard hmm, we were talking about exposing "dev only resources" when dev mode is enabled (such as the config) in another issue.

Are you seeing the feature described in this issue as something people would use in production?

If so, we can't expose the config unconditionally in dev mode.

[vorburger]

I'm interested in this topic as well, and have given it some thought...

Not actually convinced we even need "real S2I" in this scenario (as in my #1358 for native, non-dev) - in this use case, we technically don't want (need) to be "building" a new container image (which is what S2I is for), do we? What we really want is just to run quarkus:dev in-container, don't we? I'm exploring that in master...vorburger:issue-1390_dev-container ... currently stuck with #1449.

on .class or resource changes in a specific set of directories, rsync

I was thinking of simply proposing to use oc rsync, for starters.... Full disclosure: I'm not very familiar with Odo yet, but I sort of don't see yet what you would need it for, given how easy this could actually be with this approach.

BTW Skaffold is quite interesting IMHO; I'm hoping to learn more about it soon-ish. And if we were to integrate Skaffold with Knative Build, then things could start to get interesting...

[tgrall]

@gsmet it isn’t for production.odo Is used for development, but the idea is to be able to use the container/OpenShift during development and let the user doing it with iteration (without reloading the container)

So if you have a specific flag we should be able to pass it to the S2I/supervisord to enable the dev mode in the application

[geoand]

Using odo instead of plain rsync would allow users to easily handle a Quarkus app as part of their entire architecture, meaning that the app can be linked to some service via the Service Catalog, it provides a lot of conveniences such as creating a Route and much more.

Not to mention that there is a VSCode plugin that uses odo under the covers.

[kadel]

I was thinking of simply proposing to use oc rsync, for starters.... Full disclosure: I'm not very familiar with Odo yet, but I sort of don't see yet what you would need it for, given how easy this could actually be with this approach.

ou could use oc rsync and odo watch actually does something that is similar to it, but also handles all the hassle of setting the container up, it shields users from all the complexities.

odo gives this to users in a nice user-friendly way without a need to know anything about OpenShift.
That is the main odo promise

With odo it looks like this:

$ odo component create java
$ odo watch

Now you just edit files in your ide. Odo automatically detects any changes and syncs your files into the running container in OpenShift cluster (plus handles restarts, if required). You are editing files locally, but the application is running on OpenShift.