Hello Postgres and REST in Crystal

Tagged crystal, postgres, rest  Languages bash, crystal, yaml

NOTE: This does not work with Crystal 0.25.2.

Install Crystal

brew install crystal-lang
mkdir projects/hello
shards init

Set up dependencies

    github: will/crystal-pg
    version: "~> 0.5"
    github: sdogruyol/kemal
    version: "~> 0.16.1"

Write a simple REST API

require "kemal"
require "json"
require "pg"

PG_URL = "postgres://postgres@localhost:5432/xxx"
DB     = PG.connect PG_URL

get "/" do |env|
  env.response.content_type = "application/json"
  users = DB.exec("SELECT * FROM users")
  users.to_hash.map do |user|
    {first_name: user["first_name"].as(String), last_name: user["last_name"].as(String)}


How to debug Ansible variables

Tagged ansible, debug, hostvars, variables  Languages bash, yaml

Print all variables for all hosts from the command line:

 $ ansible -i inventory/local -m debug -a "var=hostvars" all

Replace hostvars with any of the following to print:

  • ansible_locals
  • groups
  • group_names
  • environment
  • vars
  • ansible_sucks

Print all variables for all hosts from a playbook:

- hosts: all
    -  debug:
        var: hostvars[inventory_hostname]
        # -vvv to debug !!!!
        # verbosity: 4

Print all variables:

- name: print ansible_local
  debug: var=ansible_local

Ansible: How to find the IP address of a specific network interface when there are multiple network interfaces

Tagged ansible, ip address, network  Languages yaml

Here’s how to find the IP address of a specific network interface that matches a given CIDR:

- hosts: all
  gather_facts: false
    - set_fact:
        prod_ip_addr: "{{ item }}"
      when: "item | ipaddr('')"
      with_items: "{{ ansible_all_ipv4_addresses }}"
    - debug: var=prod_ip_addr

This is useful for example when you have a separate management network interface.

It’s almost as easy as trying to explain what the script is doing in plain English.