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- CPS-821Getting issue details... STATUS
Description/Scope
The scope of this spike is to ascertain:
- How to use messaging (producer, agree topic etc))
- Using existing rest endpoint with additional flag indicating async response
- Also consider asynchronous request option using messaging in the proposal
Associated Jira Created for Implementation
Issues/Decisions
# | Issue | Notes/Jira | Decision |
---|---|---|---|
1 | What topic to use for client? | Topic provided by client as a parameter which will be injected into our environment and used for asynchronous requests sent back to client. | To be supplied by cient |
2 | What topic to use for private DMI-NCMP? | e.g. ncmp-async-private but decision needs to be made with current best practices. Contact Fiachra Corcoran regarding ONAP conventions. | |
3 | Are adding a new REST endpoint for async or modifying an existing endpoint? | To facilitate asynchronous requests to DMI we will need to either create a new endpoint or modify existing endpoint to include /async flag. The second solution may not be backwards compatible. However creating a new endpoint solely for a flag is also not ideal. We could add async to list of options (but this might interfere with the purpose of /options. Additionally, considered adding a new endpoint for async which simply re-routes the response to the original endpoint while adding the logic for OK response to the client. However, would this lead to a change in the schema? If so, would this be backwards compatible? | /ncmp/v1/data/ch/123ee5/ds/ncmp-datastore:*?topic=<topic-name> |
4 | Agree URL for async once #2 is clarified | CPS R10 Release Planning#NCMPRequirements #11. Based on this additional path parameter we no longer require additional /async flag in url. | /ncmp/v1/data/ch/123ee5/ds/ncmp-datastore:*?topic=<topic-name> |
5 | Passthrough request need to be able to handle different response types (using accept header) but the async option would have a fixed and possibly different response type. | CPS R10 Release Planning#NCMPRequirements #11. | We should, by default, be able to accept multiple contnet-types. |
6 | Should we create a standalone app to demo or are tests sufficient? | CSIT tests may require more involved effort - perhaps we could add standalone app to nexus and use it as part of CSIT test? | see #13 |
7 | Do we need to persist the generated requestID? | We should be be stateless | No |
8 | Error Reporting - Topic Correctness/Availability | At a minimum we should report to the client if a topic was not found or if the topic name was incorrect | In Scope |
9 | Error Reporting - Kafka Issues | Issues such full buffer/queue, drop messages, failure not in scope | Out of scope |
10 | Async Request Option using Messaging | See: https://wiki.onap.org/display/DW/CPS-821+Spike%3A+Support+Async+read-write+operations+on+CPS-NCMP+interface#CPS821Spike:SupportAsyncreadwriteoperationsonCPSNCMPinterface-AsyncRequestOptionusingMessaging(OutofScope) | Out of scope |
11 | Do we actually require futures in this implementation proposal? | It could be argued that the need for futures is made redundant by the fact we call dmi from ncmp through rest and the response will be consumed via Kafka. What benefit would future give us in this case? | Not needed |
12 | ID Generation | Which mechanism to use? Look at CPS-Temporal and follow to keep consistency | |
13 | Are there any Kafka specific environment variables or config variables to be set for this work? | We will need to add new topic for DMI → NCMP M2M Kafka - which file(s)? | |
14 | Can robot framework verify if Kafka events have been sent/received | This would be less work and overhead (rather than creating/.maintaining client app) | |
15 | Can Webflux do this work with less code/impl? | Sourabh Sourabh suggested using this to compliment our existing approach. By adding webflux we add an event loop to synchronise and access I/O connections to the database. | |
16 | ONAP may be deprecating PLAINTEXT for Kafka. Strimzi Kafka might need to be used | ||
17 | we are planning to potentially introduce a lib that clients could use to communicate directly with kafka. So not REST based but kafka native. | I believe this does not impact us as the client is outside of our scope and how they wish to communicate with Kafka is up them. |
Proposed Design
High-level Steps/Possible Tickets:
- Modify REST endpoint to include param topic (1)
- Add logic to send response and request (2a & 2b)
- Add producer to DMI (implementation and config) (31 & 3b)
- Add consumer to NCMP (implementation and config) (4a)
- Add consumer to NCMP (implementation and config) (4b)
- Demo & Test (5)
Kafka config & Implementation
Example Kafka Consumer Implementation from CPS-Temporal
The below code snippet taken from cps-temporal can be used in the same way in NCMP to listen to message from DMI substituting the topics and errorHandler
Example Kafka Consumer Config from CPS-Temporal
Example Kafka Producer Implementation from CPS-NCMP
Example Kafka Producer Config from CPS-NCMP (application.yml)
Example Kafka Docker-Compose
Future or alternative (Out of Scope)
What are Futures?
A Java Future, java.util.concurrent.Future
, represents the result of an asynchronous computation. When the asynchronous task is created, a Java Future
object is returned. This Future
object functions as a handle to the result of the asynchronous task. Once the asynchronous task completes, the result can be accessed via the Future
object returned when the task was started
source: http://tutorials.jenkov.com/java-util-concurrent/java-future.html
CompletableFuture (Java8+)
Java 8 introduced the CompletableFuture class. Along with the Future interface, it also implemented the CompletionStage interface. This interface defines the contract for an asynchronous computation step that we can combine with other steps.
CompletableFuture is at the same time a building block and a framework, with about 50 different methods for composing, combining, and executing asynchronous computation steps and handling errors.
source: https://www.callicoder.com/java-8-completablefuture-tutorial/
Alternatives - Thread
# | Type | Pros | Cons | Recommend |
---|---|---|---|---|
1 | Future | Futures return value | Y | |
2 | Thread | threads does not return anything as the run() method returns void . We could possibly implement mechanism to trigger a response but this is unnecessary as futures do this | N |
RequestID Generation
Type | Method | Ease of implementation | Decision |
---|---|---|---|
UUID |
| Easy | ~ |
Custom | We generate our own | Medium - Hard | N |
HTTP Request ID | ~ | ||
Kafka ID | ~ |
Async Request Option using Messaging (Out of Scope)
This was for a future completely message driven solution (for now we start with a REST request that will generate an async message eventually. In future we could also send a message that will trigger the same.
Webflux Investigation
What is Webflux?
Spring WebFlux is a web framework that’s built on top of Project Reactor, to give you asynchronous I/O, and allow your application to perform better. The original web framework included in the Spring Framework, Spring Web MVC, was purpose-built for the Servlet API and Servlet containers. The reactive-stack web framework, Spring WebFlux, was added later in version 5.0. It is fully non-blocking, supports Reactive Streams back pressure, and runs on such servers as Netty, Undertow, and Servlet 3.1+ containers.
We suggest that you consider the following specific points:
If you have a Spring MVC application that works fine, there is no need to change. Imperative programming is the easiest way to write, understand, and debug code. You have maximum choice of libraries, since, historically, most are blocking.
In a microservice architecture, you can have a mix of applications with either Spring MVC or Spring WebFlux controllers or with Spring WebFlux functional endpoints. Having support for the same annotation-based programming model in both frameworks makes it easier to re-use knowledge while also selecting the right tool for the right job.
A simple way to evaluate an application is to check its dependencies. If you have blocking persistence APIs (JPA, JDBC) or networking APIs to use, Spring MVC is the best choice for common architectures at least. It is technically feasible with both Reactor and RxJava to perform blocking calls on a separate thread but you would not be making the most of a non-blocking web stack.
If you have a Spring MVC application with calls to remote services, try the reactive
WebClient
. You can return reactive types (Reactor, RxJava, or other) directly from Spring MVC controller methods. The greater the latency per call or the interdependency among calls, the more dramatic the benefits. Spring MVC controllers can call other reactive components too.If you have a large team, keep in mind the steep learning curve in the shift to non-blocking, functional, and declarative programming. A practical way to start without a full switch is to use the reactive
WebClient
. Beyond that, start small and measure the benefits. We expect that, for a wide range of applications, the shift is unnecessary. If you are unsure what benefits to look for, start by learning about how non-blocking I/O works (for example, concurrency on single-threaded Node.js) and its effects.
Source: https://docs.spring.io/spring-framework/docs/current/reference/html/web-reactive.html
Webflux supports:
- Annotation-based reactive components
- Functional routing and handling
Pros & cons
Pros | Cons |
---|---|
|
|
Example
Links to materials
https://www.baeldung.com/spring-webflux
https://www.youtube.com/watch?v=1F10gr2pbvQ
Kafka Strimzi Investigation
Demo/Test
Existing Groovy tests exist for Kafka in cps-service/src/test/groovy/org/onap/cps/notification
- CPS-834Getting issue details... STATUS
To facilitate demo and testing of this functionality a new standalone app will be required to act as client.
This is necessary as the client will need to connect to Kafka to consume async responses.