Category: Tech Notes

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Using Netflix Eureka with Spring Cloud / Spring Boot microservices

I’ve been taking a look at this article on using Spring Cloud‘s integration/support for Netflix Eureka. I’ve started to put together a simple example using Eureka as a service registry for a couple of Spring Boot services, and what this would look like if deployed in Docker containers.

So far I’ve created the initial service that uses Spring Cloud’s @EnableEurekaServer annotation to start up the Eureka service.

Jumping ahead of the instructions, by default if you run this app it will attempt to reach out and find a local running Eureka server and register with it, but since this app is the Eureka server, you need to add config to tell the app not to do this by default. Otherwise you’ll see errors like:

com.sun.jersey.api.client.ClientHandlerException: java.net.ConnectException: Connection refused
at com.sun.jersey.client.apache4.ApacheHttpClient4Handler.handle(ApacheHttpClient4Handler.java:187) ~[jersey-apache-client4-1.19.1.jar:1.19.1]
at com.sun.jersey.api.client.filter.GZIPContentEncodingFilter.handle(GZIPContentEncodingFilter.java:123) ~[jersey-client-1.19.1.jar:1.19.1]
at com.netflix.discovery.EurekaIdentityHeaderFilter.handle(EurekaIdentityHeaderFilter.java:27) ~[eureka-client-1.6.2.jar:1.6.2]

Adding the recommended config per the article:

server:

  port: ${PORT:8761}

eureka:

  client:

    registerWithEureka: false

    fetchRegistry: false

    server: waitTimeInMsWhenSyncEmpty: 0

Now when I start up I see this:

2017-04-11 22:23:17.040  INFO 37607 - o.s.c.n.eureka.InstanceInfoFactory       : Setting initial instance status as: STARTING
2017-04-11 22:23:17.100  INFO 37607 - com.netflix.discovery.DiscoveryClient    : Initializing Eureka in region us-east-1
2017-04-11 22:23:17.101  INFO 37607 - com.netflix.discovery.DiscoveryClient    : Client configured to neither register nor query for data.
2017-04-11 22:23:17.110  INFO 37607 -com.netflix.discovery.DiscoveryClient    : Discovery Client initialized at timestamp 1491974597110 with initial instances count: 0
2017-04-11 22:23:17.192  INFO 37607 - c.n.eureka.DefaultEurekaServerContext    : Initializing ...
2017-04-11 22:23:17.195  INFO 37607 - c.n.eureka.cluster.PeerEurekaNodes       : Adding new peer nodes [http://localhost:8761/eureka/]
2017-04-11 22:23:17.359  INFO 37607 - c.n.d.provider.DiscoveryJerseyProvider   : Using JSON encoding codec LegacyJacksonJson
2017-04-11 22:23:17.359  INFO 37607 - c.n.d.provider.DiscoveryJerseyProvider   : Using JSON decoding codec LegacyJacksonJson
2017-04-11 22:23:17.359  INFO 37607 - c.n.d.provider.DiscoveryJerseyProvider   : Using XML encoding codec XStreamXml
2017-04-11 22:23:17.359  INFO 37607 - c.n.d.provider.DiscoveryJerseyProvider   : Using XML decoding codec XStreamXml
2017-04-11 22:23:22.479  INFO 37607 - c.n.eureka.cluster.PeerEurekaNodes       : Replica node URL:  http://localhost:8761/eureka/
2017-04-11 22:23:22.486  INFO 37607 - c.n.e.registry.AbstractInstanceRegistry  : Finished initializing remote region registries. All known remote regions: []
2017-04-11 22:23:22.486  INFO 37607 - c.n.eureka.DefaultEurekaServerContext    : Initialized

Hitting http://localhost:8761 I get the fancy Eureka dashboard:

Looks good so far! More to come later.

Github repo for the code so far is here.

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Deploying a git subtree to Heroku (or other PaaS)

Most of the common PaaS platforms like OpenShift and Heroku deploy code based on a source in a git repo – you push your local repo containing source to the remote repo on the platform, the build is performed remotely and then deploys the built artifacts.

What if you want to deploy an app that is prebuilt, or you have a git repo that contains various subfolders, and only part of the folder structure in the repo is what you need deployed?

I’ve been experimenting with a simple React app that also has a node.js backend. In hindsight restructuring the source tree to make the app easier to deploy may have been simpler, but it turns out you can push part of your source subtree to a remote repo, like an application deployed to Heroku, using ‘git subtree’:

git subtree push –prefix subfoldername heroku master

This is discussed in this post here.

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Adding react-bootstrap to a React app

Adding Bootstrap to an existing or new React app is not as obvious or easy as you would think, because of Bootstrap’s dependencies on other libraries, like jQuery (and see answers to Quora question here).

The react-bootstrap module is a React specific implementation of Bootstrap that provides JSX components for a number of the Bootstrap provided styles and components, and even layout CSS encapsulated as JSX components like: <Grid>, <Row> and <Col>

Installing it via npm is as simple as:

npm intall --save react-boostrap

You then import what you need from the module like:

import {Bootstrap, Grid, Row, Col} from 'react-bootstrap';

and then you quickly discover that the CSS based layout is not working like you’d expect. If you check the Getting Started section it mentions:

Because React-Bootstrap doesn’t depend on a very precise version of Bootstrap, we don’t ship with any included css. However, some stylesheet is required to use these components. How and which bootstrap styles you include is up to you, but the simplest way is to include the latest styles from the CDN.

Ok. So you can follow their example and load from the Bootstrap (or other) CDN, but what if you want to manage Bootstrap as an npm module too? This question is answered in this post here. What you need is to install bootstrap:

npm install --save bootstrap

and then include it into your main App.jsx with:

import 'bootstrap/dist/css/bootstrap.css';
import 'bootstrap/dist/css/bootstrap-theme.css';

and you’re up and running. Not that obvious but once you’ve setup this once, probably makes more sense the next time.

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Appending values to the end of a file from a Unix shell

Some things you do repeatedly from a *nix shell are incredibly useful and time-saving that you do them without thinking about it. Say for example you need to add a file or directory name to a file like .gitignore. On Windows you might open an editor and add the new lines to the end of the file and save it, but in a *nix shell (I imagine there’s a comparable approach maybe using something like Windows Powershell too), you can do:

echo "newfile" >> .gitignore

and you’re done.

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