Tag Archives: spring-days

advanced spring boot with consul – live blogging from spring days

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Advanced Spring Boot with Consul
Speaker: Michael Gendelman @MikeGendelman
See list of all blog posts from conference

“when someone writes something clever and leaves, that’s a problem”

“every time someone logs onto a box at a Fortune 500 company, it is a big deal”

Consul

  • for service discovery and configuration management
  • Consul agent – does health check and forwards queries. Runs on machine of all apps
  • Consul server – elects a leader. Want 3-5 per data center. Must have at least 3 so can elect leader
  • Has UI – can see properties/services/etc. Can update config in UI in addition to through yml files [talked about risk of having the real properties be out of sync of the yaml. Good that devops has evolved to the point this is a common worry]
  • Same executable for server and agent

Monitoring
“health of the service is more important than the health of a single instance”
Don’t need a page/alert if enough are still up

Code>

  • Use spring-cloud-starter-consul-all Maven dependency – made by an independent company
  • Have dev mode so can run in isolation but test all the features
  • annotation to enable discovery
  • Have bootstrap.yml file to set up config – instead of application.yml

thinks there is plugins/script to link version control to properties. good if need different properties in different environments

I learned enough about Spring Boot yesterday to be able to follow Mike’s example. Seeing the live demo of Consol was nice.

reactive programming by example – live blogging from spring days

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Reactive Programming by Example: Intro to Pivotal Reactor
Speaker: Victor Grazi @vgrazi
https://github.com/vgrazi/reactive-demo
See list of all bog posts from conference

What is Reactive

  • Think in streams – but more powerful than Java 8 streams
  • reactive streams – high performance, async stream processing non-blocking back pressure – when ready to stop getting data
  • declarative
  • doesn’t vary much by language

Maven dependencies

  • reactor-core
  • reactor-test – ex: simulate waiting X seconds without actually waiting

Everything is a stream of messages – ex: events, query results, exceptions (errors aren’t special; still a message)
Publisher – Flux emits event messages (Observable in rx-java), immutable
Subscriber – gets next message and handles events on error/complete/subscribe. doOnNext() is like peek() in Java 8 for debugging

Marble diagram

  • treat events as marbles
  • Website: http://rxmarbles.com – can see different operations and drag marbles (on a computer; doesn’t work on iPad)

Creating a flux
Flux.just(singleValue)
Flux.fromIterable/fromArray – to transform from collection/array
Flux.range(startNumber, numberOfElementsInRange)
Flux.interval(Duration.ofSeconds(n)) – emit a value every X seconds
Flux.merge – combine streams
Flux.withLatestFrom – unlike zip, get latest available element rather than getting the “next” one
Flux.create – use lambda to create a listener with logic for publishing elements

Transformations
take
skip
distinct
distinctUntilChanged-only eliminate adjacent duplicates
filter
map
flatMap
zipWith – combine existing stream with another stream in tuples
sort

Differences from Java streams

  • push based,not pull based
  • Attached to real time feeds
  • Conncurrent
  • Back pressure
  • Can only use once
  • Can compose streams (zip/merge)
  • Can fully work with infinite streams

Cold vs Hot Flux
Cold streams are finite, known elements. Hot streams are more realistics

Must call subscribe for anything to happen (like a terminal operator in Java 8 streams)

I learned a lot. Or reviewed a lot and learned some. Having heard this,I realize I had heard some of it before. Also, while the concepts are different than Java 8, knowing Java 8 streams really well helps retain this. The syntax similarities help. As do learning the key differences vs learning every API and not thinking about streams at all. And the demo at the end was easy to follow. This presentation reminds me of Java 8 streams in that it took me a few presentations by different people to finally grok it well.

servlet vs reactive stacks – live blogging from spring days

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Servlet vs Reactive Stacks in 5 Use Cases
Speaker: Rossen Stoyanchev
See list of all blog posts from conference

Asynchronous

  • asynch is a perception from the beholder. For example, HTTP is synchronous but looks async from the server. [i’m a little confused but i think i get the point of this example]
  • Amount of asynchronity is growing. The more you do it, the more complex it becomes
  • Puting blocking component behind a thread pool makes async because now there is a callback
  • Different to do async throughout the app vs one callback in one place

Elastic thread pool
<ul

  • absorb latency of blocking call
  • can be difficult to configure because need enough threads for the number of slow clients so can absorb lateny
  • uses memory from increasing call stack for threads especially at scale.
  • strategy works, but doesn’t scale

Event loop

  • Have only one thread
  • Model is non-blocking

This is how modern HTTP servers work – certain number worker threads and event loop delegates to them

Reactive

  • brings flow control/li>
  • Scale without adding more threads

Java 9 Flow is closest built in option but need library for implementation.Ex Reactor, RxJava

Reactive Stack
Need Spring 5

  • Netty/Servlet 3.1+/Undertow
  • Reactive Streams Reactor
  • Spring WebFlux

Servlet Stack
Need Servlet 3 for async

  • Servlet container
  • Servlet API
  • Spring MVC

The use cases were live examples. It was cool that the Flux API looks like Java 8 streams code.

Showed how backpressure prevents adding more when not ready.

I like the @Tailable annotation – it shows what you can tail the results of while running.

Overall, I learned/reviewed some basics. The use cases were too fast for me to follow. Which is a sign I need to read a book about reactive. I’ve seen some presentations, but I don’t remember enough to recall all the terms fast enough to follow the code examples. That said,live demos are fun.