[Short Tip] Handling “can’t concat str to bytes” error in Ansible’s uri module

When working with web services, especially REST APIs, Ansible can be of surprising help when you need to automate those, our want to integrate them into your automation.

However, today I run into a strange Python bug while I tried to use the uri module:

An exception occurred during task execution. To see the full traceback, use -vvv. The error was: TypeError: can't concat str to bytes
fatal: [localhost]: FAILED! => {"changed": false, "content": "", "elapsed": 0, "msg": "Status code was -1 and not [200]: An unknown error occurred: can't concat str to bytes", "redirected": false, "status": -1, "url": "https://www.ansible.com"}

This drove me almost nuts because it happened on all kinds of machines I tested, even with Ansible’s devel upstream version. It was even independent of the service I targeted – the error happened way earlier. And a playbook to showcase this was suspiciously short and simple:

---                                 
- name: Show concat str byte error  
  hosts: localhost                  
  connection: local                 
  gather_facts: no                  
                                    
  tasks:                            
    - name: call problematic URL call
      uri:                          
        url: "https://www.ansible.com"
        method: POST                
        body:                       
          name: "myngfw"

When I was about to fill an issue at Ansible’s Github page I thought again and wondered that this is too simple: I couldn’t imagine that I was the only one hitting this problem. I realized that the error had to be on my side. And thus meant that something was missing.

And indeed: the body_format option was not explicitly stated, so Ansible assumed “raw”, while my body data were provided in json format. A simple

        body_format: json

solved my problems.

Never dare to ask me how long it took me to figure this one out. And that from the person who write and entire how to about how to provide payload with the Ansible URI module….

[Short Tip] Provide dictionaries as default in Ansible variables

Ansible uses the Jinja2 template engine to handle variables. This includes the default filter, which sets a default value if a referenced variable is not explicitly defined somewhere else.

With Ansible it might happen that instead of a skalar variable a key-value is needed, a dictionary. If you just paste the plain text in there, you might run into trouble:

fatal: [test.example.com]: FAILED! => {"changed": false, "msg": "argument env is of type and we were unable to convert to dict: dictionary requested, could not parse JSON or key=value"}

The key-value pair needs to be properly formatted:

"{{ my_variable|default({'key':'value'}) }}"

Thanks to @bcoca for his post about this.