CONTINUAL INTEGRATION

Problem scenario
You run an Ansible playbook but you get an error about "this one looks like it might be an issue with missing quotes."  Your Ansible playbook compares two variables with each other.  

After running ansible-playbook on the .yaml file, you get this error:

"ERROR! Syntax Error while loading YAML.
  expected <block end>, but found '<scalar>'

The error appears to have been in '/home/cooluser/good.yaml': line 12, column 36, but may
be elsewhere in the file depending on the exact syntax problem.

The offending line appears to be:

  - shell: echo "THIS STATEMENT IS EXECUTED" > /tmp/printer.txt
    when: "{{ ansible_hostname }}" == "{{ ansible_nodename }}"
                                   ^ here
We could be wrong, but this one looks like it might be an issue with
missing quotes.  Always quote template expression brackets when they
start a value. For instance:

    with_items:
      - {{ foo }}

Should be written as:

    with_items:
      - "{{ foo }}""

How do you get the comparison to work?

Solution
Put single quotes around the entire expression including the == (or !=) symbol.  

Example of an incorrect when (if) statement:

  - shell: echo "THIS STATEMENT IS EXECUTED" > /tmp/printer.txt
    when: "{{ ansible_hostname }}" == "{{ ansible_nodename }}"

The above has two variables on each side of an equivalence condition.  With Ansible 2.1, it will throw an error.

Here is an example of a correct when: statement (with single quotes around everything except the "when:"):

  - shell: echo "THIS STATEMENT IS EXECUTED" > /tmp/printer.txt
    when: '"{{ ansible_hostname }}" == "{{ ansible_nodename }}"'

Problem scenario
You want an Ansible playbook to run on specific managed nodes.  You can create a list of the servers you want the playbook to apply to.  How do you provide a list of specific hostnames and have the Ansible playbook run on each server?

Prerequisites
This assumes that you have installed Ansible and have it working with the managed nodes you want to run a playbook on.  For directions on deploying Ansible, see this posting.

Procedures
You could modify the inventory file on your Ansible server.  But if you want a list for an ad hoc run of an Ansible playbook, do the following:

1.  In the .yaml or .yml file of your playbook, create a stanza like this:

hosts:  coolgroupofservers

2.  Create a file with an arbitrary name in the same directory as your playbook.  Call it something like foobar.txt

3.  Have foobar.txt have the following content:

[coolgroupofservers]
FQDN1
FQDN2
FQDN3

4.  Run the Ansible playbook (e.g., goodpb.yaml) with the -i flag to call the foobar.txt file:

ansible-playbook goodpb.yaml -i foobar.txt