This blog entry describes an approach to adopt Continuous Delivery for Vert.x applications using Jenkins and Ansible by taking advantage of the Jenkins Job DSL and Ansible plugins.

Table of contents

• Preamble
• Introduction
• Overview
• Creating a Jenkins build job using Job DSL
• Deploying Vert.x app using Ansible
• Sample sources and demo
  • Launch instructions
  • Demo
• Conclusion

Preamble

This post was written in context of the project titled “DevOps tooling for Vert.x applications“, one of the projects at Vert.x taking place during the 2016 edition of Google Summer of Code, a program that aims to bring students together with open source organizations in order to help them to gain exposure to software development practices and real-world challenges.

Introduction

System configuration management (e.g., Ansible) has been really hype in the recent years and there is a strong reason for that. Configuration management facilitates configuring a new environment following a fixed recipe or slightly varying it with the help of parameters. This has not only the advantage of being able to do it more frequently but reduces the chance of errors than doing it manually.
Beyond that, combining it with Continuous Integration tools (e.g., Jenkins) allows making a deployment as soon as a new codebase version is available, which represents the main building block of a Continuous Delivery pipeline, one of the objectives of embracing a DevOps culture.

Given that Vert.x is a framework that consists in a few libraries which can be shipped within a single fat jar, adopting a DevOps culture while developing a Vert.x-based application is straightforward.

Overview

As seen in the diagram below, this post describes a method to define a Jenkins build job which will react to changes in a code repository. After succesfully building the project, the job will execute an Ansible playbook to deploy the new application version to the hosts specified within the Ansible configuration.

Creating a Jenkins build job using Job DSL

Jenkins has created a convenient way to define build jobs using a DSL. While this option avoids the hassle of configuring build jobs manually, it supports all features of the regular interface through its API. It is possible to use Ansible together with Jenkins with the help of the Ansible plugin, whose instructions are also included in the Job DSL API. Alternatively to the Job DSL Plugin, Ansible can be used inside the definition of Jenkins Pipeline, one of tool’s most recent features.

Below is a sample job definition which can be used after creating a freestyle job (seed job) and adding a new build step with the DSL script. In the script, there are a few things to notice:

• A name for the job created by the seed job is given.
• Specific versions of JDK, Maven, and Ansible (available in the environment) are used.
• Git is selected as the SCM platform and the target repository is defined. Also, the build job is triggered according to a specific interval.
• The Maven package goal is invoked, which is instructed to package the application into a fat jar.
• Lastly, Ansible is used to call a playbook available in the filesystem. The app will be deployed to the defined target hosts and the credentials (configured in Jenkins) will be used to log into the target hosts. Additionally, enabling the colorizedOutput option will result in a friendlier formatting of the results in the console output. The contents of this playbook will be addressed in the next section.

job('vertx-microservices-workshop-job') {
    jdk('JDK8')
    scm {
        git('git://github.com/ricardohmon/vertx-microservices-workshop.git')
    }
    triggers {
        scm('*/15 * * * *')
    }
    steps {

      def mvnInst = 'M3.3.9'  
      maven {  
        goals('package')  
        mavenInstallation(mvnInst)  
      }  
      ansiblePlaybook('/ansible/playbook.yml') {  
        inventoryPath('/ansible/hosts')  
        ansibleName('Ansible2.0')  
        credentialsId('vagrant-key')  
        colorizedOutput(true)  
      }  

    }  
}

Deploying Vert.x app using Ansible

An Ansible Playbook results quite convenient to deploy a Vert.x application to a number of hosts while still taking considerations for each of them. Below is a sample playbook that deploys the respective application to each of the hosts described in an inventory file. The playbook comprises the following tasks and takes the listed considerations:

1) A task that targets only hosts with a database.

• The target hosts is specified with the name of the host (or hosts group) defined in the inventory file.

2) Actual application deployment task. Here, several considerations are done:

• The application may require that only one host is updated at the time.
  This can be achieved with the serial option, while the order of the deployment to hosts can be enforced in the hosts option.
  

  Host processing order Even though we could have declared all hosts, Ansible does not provide an explicit way to specify the order.

• Java is a system requirement for our Vert.x applications.
  Besides installing it (keep reading), we need to declare the JAVA_HOME environment variable.
• A deployment may just represent an update to an already running application (Continuous Deployment), hence it is convenient to stop the previous application inside the pre_tasks and take post-deployment actions in the post_tasks. Vert.x ships with the convenient start/stop/list commands that result very helpful here. We can use the list command and extract (using regex) the id of the running application of its output to stop it before deploying a new version.

  Hint If our solution includes a load balancer or proxy, we could deal with them at this step as described in Ansible’s best practices for rolling updates

• Call to a role that makes the actual application deployment. The Jenkins Ansible Plugin includes, between others, a WORKSPACE environment variable, which may result very helpful in the following tasks, as shown later.

# 1) Special task for the service with a db
- hosts: audit-service
  remote_user: vagrant
  become: yes
  roles:
    - db-setup

  # 2) Common tasks for all hosts
- hosts: quote-generator:portfolio-service:compulsive-traders:audit-service:trader-dashboard
  remote_user: vagrant
  become: yes
  serial: 1
  environment:
    JAVA_HOME: /usr/lib/jvm/jre-1.8.0-openjdk/

  pre_tasks:
  - name: Check if the app jar exists in the target already
    stat: path=/usr/share/vertx_app/app-fatjar.jar
    register: st
  - name: List running Vert.x applications
    command: java -jar /usr/share/vertx_app/app-fatjar.jar list
    register: running_app_list
    when: st.stat.exists == True
  - name: Stop app if it is already running (avoid multiple running instances)
    command: java -jar /usr/share/vertx_app/app-fatjar.jar stop {{ item | regex_replace('^(?P<V_id>.[8]-.[4]-.[4].[4].[12])\t.*', '\\g<V_id>') }}
    with_items: "{{ running_app_list.stdout_lines|default([]) }}"
    when: st.stat.exists == True and (item | regex_replace('.*\t(.*)$', '\\1') | match('.*/app-fatjar.jar$'))

  # Main role
  roles:
    - { role: vertx-app-deployment, jenkins_job_workspace: "" }

  post_tasks:
  - name: List again running Vert.x applications
    command: java -jar /usr/share/vertx_app/app-fatjar.jar list

Once we took care of the actions shown before, the remaining tasks (included in the main deployment role) reduce to the following:

1) Prepare the target machine with the proper environment to run our application. This includes:

• Set up Java (pretty convenient to do it through a package manager).
• Copy the Vert.x application package to the appropriate folder (quite simple using a fat jar). The actual name and location of the jar package in the Jenkins environment can be defined using host-specific variables.
• In case necessary, copy the required config files.

- name: Install Java 1.8 and some basic dependencies
  yum: name={{ item }} state=present
  with_items:
   - java-1.8.0-openjdk
- name: Ensure app dir exists
  file: path=/usr/share/vertx_app/ recurse=yes state=directory mode=0744
- name: Copy the Vert.x application jar package
  copy: src={{ app_jar }} dest=/usr/share/vertx_app/app-fatjar.jar mode=0755
- name: Ensure config dir exists
  file: path=/etc/vertx_app/ recurse=yes state=directory mode=0744
- name: Copy the application config file if needed
  copy: src={{ app_config }} dest=/etc/vertx_app/config.json mode=0755
  when: app_config is defined

2) Run the application as a service in the hosting machine.

• Make sure to ignore the hang up signal with the help of nohup command. Otherwise, Ansible will be stuck at this step.

- name: Run Vert.x application as a service, ignore the SIGHUP signal
  shell: nohup java {{ vertx_opts }} -jar /usr/share/vertx_app/app-fatjar.jar start {{ launch_params }}
  register: svc_run_out
- name: Print run output
  debug: var=svc_run_out.stdout_lines

This describes all the configuration needed to be able to build from a repository using Jenkins and deploy the results to our hosts with Ansible.

Sample sources and demo

The sample configurations presented before are part of a complete demo focused on the Vert.x microservices workshop to exemplify a basic Continuous Delivery scenario. This set up is available in a repository and contains, in addition, a pre-configured Jenkins-based demo ready to host the build job described the previous sections. The demo scenario requires Vagrant and Virtualbox to be launched.

Launch instructions

• Clone or download this repository, and launch the demo using vagrant up

  git clone https://github.com/ricardohmon/vertx-ansible.git
  cd demo
  vagrant up

  This command will launch a virtual machine hosting Jenkins with the required plugins installed (tools names needed) and also launch five additional VMs that will host the microservices deployed by Jenkins.

• Create a Jenkins freestyle build job using the DSL job script (seed job) found in deployment-jobs/microservices_workshop_dsl.groovy and build it.

  Tool configuration assumption The DSL Job assumes the following tools (with names) have been configured in Jenkins: Java 8(JDK8), Maven (M3.3.9), Ansible (Ansible2.0)

• After building the seed job, a new job(vertx-microservices-workshop-job) will be created, which will be in charge of pulling recent changes of the project, building it, and deploying it.

Demo

Watch the previous demo in action in the following screencast:

Conclusion

Continuous Delivery approach is a must in modern software development lifecycles (including Vert.x-based applications) and a step further towards adopting a DevOps culture. There are a number of tools that enable it and one example is the combination of Jenkins + Ansible described in this post.
While Jenkins offers the possibility to integrate recent changes perceived in a codebase and build runnable artifacts, Ansible can help to deploy them to hosting environments. The usage of both tools can be coupled easily with the help of the Job DSL plugin, a feature of Jenkins that allows describing a build job using a domain-specific language, which can help to integrate additional steps and tools to a _CD_ pipeline.

Further enhancements can be done to this basic pipeline, such as, integrating the recent Pipeline plugin, a feature that allows a better orchestration of CD stages; inclusion of notification and alerting services; and, ultimately a zero-downtime deployment approach, which could be achieved with the help of a proxy; plus, tons of options available trough Jenkins plugins.

Thanks for reading!