Tuesday, July 19, 2016

Introducing "Yet another" Cloud foundry Gradle plugin

In the process of working on an automated Jenkins pipeline for deploying a Cloud Foundry application with two of my colleagues(Thanks Mark Alston, Dave Malone !) I decided to try my hand on writing a Gradle plugin to perform some of the tasks that are typically done using a command line Cloud Foundry Client.

Introducing the totally unimaginatively named "ya-cf-app-gradle-plugin" with a set of gradle tasks(dare I say opinionated!) that should help automate some of the routine steps involved in deploying a java application to a Cloud Foundry environment. The "ya" or the yet-another part is because this is just a stand-in plugin, the authoritative plugin for Cloud Foundry will ultimately reside with the excellent CF-Java-Client project.

I have provided an extensive README with the projects documentation that should help in getting started with using the plugin, the tasks should be fairly intuitive if you have previously worked with the CF cli.

Just as an example, once the gradle plugin is cleanly added into the build script, the following gradle tasks are available when listed by running "./gradlew tasks" command:

All the tasks work off a configuration provided the following way in a cfConfig block in the buildscript:

apply plugin: 'cf-app'

cfConfig {
 //CF Details
 ccHost = "api.local.pcfdev.io"
 ccUser = "admin"
 ccPassword = "admin"
 org = "pcfdev-org"
 space = "pcfdev-space"

 //App Details
 name = "cf-show-env"
 hostName = "cf-show-env"
 filePath = "build/libs/cf-show-env-0.1.2-SNAPSHOT.jar"
 path = ""
 domain = "local.pcfdev.io"
 instances = 2
 memory = 512

 //Env and services
 buildpack = "https://github.com/cloudfoundry/java-buildpack.git"
 environment = ["JAVA_OPTS": "-Djava.security.egd=file:/dev/./urandom", "SPRING_PROFILES_ACTIVE": "cloud"]
 services  = ["mydb"]

Any overrides on top of the base configuration provided this way can be done by specifying gradle properties with a "cf.*" pattern. For eg. a normal push of an application would look like this:

./gradlew cf-push

and a push with the name of the application and the host name overridden would look like this:

./gradlew cf-push -Pcf.name=Green -Pcf.hostName=demo-time-temp

All of the tasks follow the exact same pattern, depending on the cfConfig block as the authoritative source of properties along with the command line overrides. There is one task that can be used for retrieving back some of the details of an app in CloudFoundry, the task is "cf-get-app-detail", say after deploying a canary instance of an app you wanted to run a quick test against it, the task would look along these lines, a structure "project.cfConfig" is populated with the app details once successfully invoked:

task acceptanceTest(type: Test, dependsOn: "cf-get-app-detail")  {
 doFirst() {
  systemProperty "url", "https://${project.cfConfig.applicationDetail.urls[0]}"
 useJUnit {
  includeCategories 'test.AcceptanceTest'


1. The plugin is built on top of the excellent CF-Java-Client project
2. I have borrowed a lot of ideas from gradle-cf-plugin but is more or less a clean room implementation
3. Here is a sample project which makes use of the plugin.

Tuesday, July 5, 2016

Spring Cloud Zuul - Writing a Filter

Netflix OSS project Zuul serves as a gateway to backend services and provides support for adding in edge features like security, routing. In the Zuul world specific edge features are provided by components called the Zuul Filter and writing such a filter for a Spring Cloud based project is very simple. A good reference to adding a filter is here. Here I wanted to demonstrate two small features - deciding whether a filter should act on a request and secondly to add a header before forwarding the request.

Writing a Zuul Filter

Writing a Zuul Filter is very easy for Spring Cloud, all we need to do is to add a Spring bean which implements the ZuulFilter, so for this example it would look something like this:

import com.netflix.zuul.ZuulFilter;
import com.netflix.zuul.context.RequestContext;
import org.springframework.stereotype.Service;

public class PayloadTraceFilter extends ZuulFilter {

    private static final String HEADER="payload.trace";

    public String filterType() {
        return "pre";

    public int filterOrder() {
        return 999;

    public boolean shouldFilter() {

    public Object run() {

Some high level details of this implementation, this has been marked as a "Filter type" of "pre" which means that this filter would be called before the request is dispatched to the backend service, filterOrder determines when this specific filter is called in the chain of filters, should Filter determines if this filter is invoked at all for this request and run contains the logic for the filter.

So to my first consideration, whether this filter should act on the flow at all - this can be done on a request by request basis, my logic is very simple - if the request uri starts with /samplesvc then this filter should act on the request.

public boolean shouldFilter() {
    RequestContext ctx = RequestContext.getCurrentContext();
    String requestUri = ctx.getRequest().getRequestURI();
    return requestUri.startsWith("/samplesvc");

and the second consideration on modifying the request headers to the backend service:

public Object run() {
    RequestContext ctx = RequestContext.getCurrentContext();
    ctx.addZuulRequestHeader("payload.trace", "true");
    return null;

A backing service getting such a request can look for the header and act accordingly, say in this specific case looking at the "payload.trace" header and deciding to log the incoming message:

@RequestMapping(value = "/message", method = RequestMethod.POST)
public Resource<MessageAcknowledgement> pongMessage(@RequestBody Message input, @RequestHeader("payload.trace") boolean tracePayload) {
    if (tracePayload) {
        LOGGER.info("Received Payload: {}", input.getPayload());


As demonstrated here, Spring Cloud really makes it simple to add in Zuul filters for any edge needs. If you want to explore this sample a little further I have sample projects available in my github repo.