---  
# define name of gropus or particular hosts from inventory file
# magic constants: 
# `all` is aboul all known hosts from inventory
# `localhost` for local host (see cdocumentation for more setting)
- hosts: all
# `become` is about become someone as. usually about become sudo(or su) 
# in this case the scenario defaults for tasks will be current user
  become: no
  
# root node for defining list of tasks
  tasks:  
    - name: Install java role from Ansible Galaxy  
      # usually tasks executed to remotes nodes
      # but there are some task kinds that do execued on local machine
      # and `local_action` is kind of generic for those
      # in this case local action is a task of `command` type
      # and a command in this case is: 
      # `ansible-galaxy install geerlingguy.java`
      # `ansible-galaxy` is executable that came with ansible
      # it's kind of package manager for community-crafted recepies
      # and in this case we do install locally `geerlingguy.java` community package that is intended to install java 
      local_action: command ansible-galaxy install geerlingguy.java  
    - name: installing repo for Java 8 in Ubuntu
      # quite simple task that simply add apt repository
      # but it also interesting because of 
      # set sudo privilegies for this task
      become: yes  
      apt_repository:  
        repo: ppa:openjdk-r/ppa  
    - name: apt update  
      become: yes  
      apt:  
        update_cache: yes  
    - name: Install Java
      when: "ansible_os_family == 'Debian'"  
      vars:  
        java_packages:  
          - openjdk-8-jdk  
      # this is a task that run ansible role as a ansible role
      # ansible roles as addons from ansible galaxy
      # these addons usually run before and/or after all tasks
      # but this task allows to run role as a regular step  
      include_role:  
        name: geerlingguy.java  
        # and this relo requires to be run as sudo
        # but the script is not sudo 
        # so we apply sudo for entire role as it required
        apply:  
          become: true

---  
- hosts: all  
  become: no  
  # eventually some tasks need to know some information about target node
  # like OS installed or disk space left
  # and those information are collected on each playbook run
  # it took some time so there are options to boost that by caching unchanged facts
  gather_facts: true # default
  # change this on how tasks must run on hosts: sequential or serialized or another strategy
  strategy: linear # default
  # even if this file is declarative definition
  # it still have all the things the regular programing language have
  # like variables with different scopes, 
  # tasks results into variables writes
  # and conditions on tasks
  # in this case we simply put the file we need content as a variable
  # later on we will compare this with actual file content and 
  # perform actions depends on diference
  vars:  
    systemd_service_file: |  
      [Unit]  
      Description=App service  
        
      [Service]  
      User=root  
      Group=root  
      ExecStart=/usr/bin/java -jar /home/ubuntu/app.jar  
      # default stdout at: `sudo journalctl -u app_service`  
        
      [Install]  
      WantedBy=multi-user.target  
  
  tasks:  
    - name: Build maven artifact locally
      # Ansible is designed to execute commands on remote nodes
      # but it also can execute ones on local machine.
      # Eventually in different scenarios is needed to either 
      # call some utility, move a file, interact services, etc.
      # Below is short syntax
      local_action: shell mvn clean package
      # But also alternative full one:
      # local_action: 
      #      module: shell
      #      cmd: mvn clean package
      # Read more there:
      # https://stackoverflow.com/a/56050507/449553
      # 
    - name: Deploy artifact
      copy:  
        src: "{{ item }}"  
        dest: ~/app.jar  
        mode: u=rwx,g=rx,o=rx  
      with_fileglob:
        - "target/*.jar"  
  - name: Systemd file exists  
    become: yes  
    stat:  
      path: /etc/systemd/system/app_service.service  
      checksum_algorithm: md5  
    register: app_service_stat  
  - name: Setting facts  
    become: no  
    set_fact:  
      # since missing file has no checksum, use "false" value instead  
      remote_file_sum: "{{ app_service_stat.stat.checksum | default(false) }}"  
      # anything: "{{ as.as.as.as.as | default('not as') }}" <- works!  
      # or that: # remote_file_sum: "{{ app_service_stat.stat.exists | ternary(app_service_stat.stat.checksum, false) }}"  local_file_sum: "{{ systemd_service_file | hash('md5') }}"  
      cacheable: no # 'no' is default, if yes, will be cached on remote host/sequential playbook run  
  - name: Systemd file debug integrity  
    vars:  
      msg: |-  
          Remote systemd file exists: {{ app_service_stat.stat.exists }}  
          Remote systemd file checksum: {{ remote_file_sum }}  
          Valid systemd file checksum: {{ local_file_sum }}  
      debug:  
        # instead of printing message directly here  
        # I use task variable defined above 
        # and print that with skipping empty line (last one as a result of split) 
        # these all are just because "msg" print JSON, so \n will be "\n" 
        # but if print content as array of lines, it looks nicer  msg: "{{ msg.split('\n') | reject('match', '^$') }}"  
  - name: Creating systemd service file if changed   
    when: remote_file_sum != local_file_sum  
    become: yes  
    copy:  
      dest: "/etc/systemd/system/app_service.service"  
      mode: u=rwx,g=rx,o=rx  
      owner: root  
      group: root  
      content: "{{systemd_service_file}}"  
  - name: Start app service  
    become: yes  
    systemd:  
      name: app_service  
      enabled: yes  
      state: restarted  
      daemon_reload: yes  
  # `name` attribute is optional btw  
  - wait_for:  
      port: 80