How would you get a Spring Boot app running in Kubernetes in development mode, where it can quickly restart if there are changes to the source code? You want to keep your default settings and binary artifacts optimized for production, so you don't want to add Devtools to the build, but you want it to kick in when you ask it to, even if the app is running in a cluster.
Spring Boot has its Devtools feature, but that works best if the app is running in the same place as the code is being edited. You could run the IDE in the cluster, and that's possible with things like Code Server. If we wanted to stick with a local IDE though, Skaffold has a file sync feature. Could that work with Devtools?
Get kind running locally and a local registry on port 5000, e.g. using the utility script in this repo:
src/build/kind-setup.sh
Set up the default builder:
pack set-default-builder paketobuildpacks/builder:full
and then make a builder:
pack create-builder -c builder/builder.toml localhost:5000/packs/java
Push the image into the repository so it can be used by other tools (like skaffold):
docker push localhost:5000/packs/java
pack build demo --builder localhost:5000/packs/java
Run it:
docker run --entrypoint dev -p 8080:8080 demo
You will see the devtools starting (via logs and the restartedMain thread ID, and there should be actuators
$ curl localhost:8080/actuator/info
{"name": "foo"}
To take advantage of the devtools restarts we can deploy to Kubernetes, and let Skaffold sync the file changes:
skaffold dev --port-forward -p dev
It also works with skaffold debug, but remember to add an explicit --auto-sync to the command line. E.g:
skaffold debug --auto-sync --port-forward -p dev
Output:
Listing files to watch...
- localhost:5000/apps/demo
Generating tags...
- localhost:5000/apps/demo -> localhost:5000/apps/demo:b906cca-dirty
Checking cache...
- localhost:5000/apps/demo: Found Locally
...
Watching for changes...
[demo]
[demo] . ____ _ __ _ _
[demo] /\\ / ___'_ __ _ _(_)_ __ __ _ \ \ \ \
[demo] ( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
[demo] \\/ ___)| |_)| | | | | || (_| | ) ) ) )
[demo] ' |____| .__|_| |_|_| |_\__, | / / / /
[demo] =========|_|==============|___/=/_/_/_/
[demo] :: Spring Boot :: (v2.3.0.RC1)
[demo]
[demo] 2020-10-16 10:18:57.498 INFO 9 --- [ restartedMain] com.example.demo.DemoApplication : Starting DemoApplication on demo-c8d6f9f7d-ljlpq with PID 9 (/workspace/BOOT-INF/classes started by cnb in /workspace)
...
[demo] 2020-10-16 10:18:58.752 INFO 9 --- [ restartedMain] com.example.demo.DemoApplication : Started DemoApplication in 1.515 seconds (JVM running for 1.863)
Syncing 3 files for localhost:5000/apps/demo:c2a4a6b772d73849eb0cf37bfa0d5c14f85a883c9643e1af7cb8f037a66d22a4
Watching for changes...
If you make a change to the application, e.g. tweak the @GetMapping on the home page, you will see Skaffold copy the change over and Spring Boot will restart the app.
...
[demo] 2020-10-16 10:21:07.217 INFO 9 --- [ restartedMain] o.s.b.web.embedded.netty.NettyWebServer : Netty started on port(s): 8080
[demo] 2020-10-16 10:21:07.218 INFO 9 --- [ restartedMain] com.example.demo.DemoApplication : Started DemoApplication in 0.181 seconds (JVM running for 130.329)
[demo] 2020-10-16 10:21:07.220 INFO 9 --- [ restartedMain] .ConditionEvaluationDeltaLoggingListener : Condition evaluation unchanged
Syncing 3 files for localhost:5000/apps/demo:c2a4a6b772d73849eb0cf37bfa0d5c14f85a883c9643e1af7cb8f037a66d22a4
Watching for changes...
[demo]
[demo] . ____ _ __ _ _
[demo] /\\ / ___'_ __ _ _(_)_ __ __ _ \ \ \ \
[demo] ( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
[demo] \\/ ___)| |_)| | | | | || (_| | ) ) ) )
[demo] ' |____| .__|_| |_|_| |_\__, | / / / /
[demo] =========|_|==============|___/=/_/_/_/
[demo] :: Spring Boot :: (v2.3.0.RC1)
[demo]
[demo] 2020-10-16 10:21:23.806 INFO 9 --- [ restartedMain] com.example.demo.DemoApplication : Starting DemoApplication on demo-c8d6f9f7d-ljlpq with PID 9 (/workspace/BOOT-INF/classes started by cnb in /workspace)
[demo] 2020-10-16 10:21:23.806 INFO 9 --- [ restartedMain] com.example.demo.DemoApplication : No active profile set, falling back to default profiles: default
[demo] 2020-10-16 10:21:23.940 INFO 9 --- [ restartedMain] o.s.b.a.e.web.EndpointLinksResolver : Exposing 4 endpoint(s) beneath base path '/actuator'
[demo] 2020-10-16 10:21:23.956 INFO 9 --- [ restartedMain] o.s.b.d.a.OptionalLiveReloadServer : LiveReload server is running on port 35729
[demo] 2020-10-16 10:21:23.963 INFO 9 --- [ restartedMain] o.s.b.web.embedded.netty.NettyWebServer : Netty started on port(s): 8080
[demo] 2020-10-16 10:21:23.964 INFO 9 --- [ restartedMain] com.example.demo.DemoApplication : Started DemoApplication in 0.169 seconds (JVM running for 147.075)
[demo] 2020-10-16 10:21:23.965 INFO 9 --- [ restartedMain] .ConditionEvaluationDeltaLoggingListener : Condition evaluation unchanged