subprocess.check_output failing within Docker - python-3.x

Question

Similiar questions have been asked before, but the solutions for these questions don't resolve my own issue. I have a repo that relies on a base repo, whereby a connection is made to a neo4j database. My tests for the base repo work. The repo I have (transforms files) has already proven to work locally. When I run the repo in Docker I get a FileNotFoundError which is being thrown out from the base repo:
Base repo module
def get_docker_host_ip(self):
z = subprocess.check_output(['ip', '-4', 'route', 'list', 'match', '0/0'])
z = z.decode()[len('default via '):]
return z[: z.find(' ')]
The traceback:
Traceback (most recent call last):
File "/opt/app/src/myscript.py", line 252, in <module>
myModule = My_Module(args)
File "/opt/app/src/myscript.py", line 45, in __init__
self.neo4jadapter = Neo4jAdapter()
File "/opt/app/base/base/neo4j_adapter.py", line 19, in __init__
neo4j_host = self.get_docker_host_ip()
File "/opt/app/base/base/neo4j_adapter.py", line 51, in get_docker_host_ip
z = subprocess.check_output(['ip', '-4', 'route', 'list', 'match', '0/0'])
File "/usr/lib/python3.7/subprocess.py", line 395, in check_output
**kwargs).stdout
File "/usr/lib/python3.7/subprocess.py", line 472, in run
with Popen(*popenargs, **kwargs) as process:
File "/usr/lib/python3.7/subprocess.py", line 775, in __init__
restore_signals, start_new_session)
File "/usr/lib/python3.7/subprocess.py", line 1522, in _execute_child
raise child_exception_type(errno_num, err_msg, err_filename)
FileNotFoundError: [Errno 2] No such file or directory: 'ip': 'ip'
For subprocess.check_output, I have also added shell=True as recommended on other posts, but it doesn't make a different:
z = subprocess.check_output(['ip', '-4', 'route', 'list', 'match', '0/0'], shell=True)
This Traceback only occurs when I run the script in Docker. Where am I going wrong?

Answer 1

Thanks to #DavidMaze's comment, the ip tool needs to be installed via Docker, for example:
RUN apt-get install iproute2