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How to pass command line arguments to a python Docker container?
Before getting into the docker container arguments we must know about python command line arguments and how they are accessed by the developer. Command line arguments are of great use when we want our python script to be controlled outside of the program.
Access the python script’s command line arguments
Step 1: Create a python script main.py
Example
# sys will allow us to access the passed arguments import sys # sys.argv[0] access the first argument passed that is the python script name print("\nFile or Script Name is :", sys.argv[0]) # print arguments other than the file name print("\nArguments passed:", end = " ") for i in range(1, len(sys.argv)): print(sys.argv[i], end = " ") # Lowercase operation on the passed arguments for i in range(1, len(sys.argv)): print(sys.argv[i].lower(), end = " ")
Step 2: Run on the terminal with arguments
#python3 main.py HELLO THIS IS TUTORIALSPOINT
Output
File or Script Name is : main.py Arguments passed: HELLO THIS IS TUTORIALSPOINT hello this is tutorialspoint
Pass these arguments to the docker container
We have different ways to pass command line arguments to the docker container. Some of these are mentioned below stepwise.
Using Docker arguments with ENTRYPOINT
The trick is to use entrypoints and dockerfile and redirect that entrypoint to the python file execution. After this just pass the required python arguments during the process of running the docker container.
Step 1: Create a Dockerfile
Example
FROM python WORKDIR /app COPY . /app/ ENTRYPOINT ["python3", "main.py"]
Step 2: Build the image
Example
#docker build -t arg_py .
Output
Sending build context to Docker daemon 8.192kB Step 1/4 : FROM python ---> fa9122485d1d Step 2/4 : WORKDIR /app ---> Using cache ---> 9e9708fe1d43 Step 3/4 : COPY . /app/ ---> aea9ecf32f55 Step 4/4 : ENTRYPOINT ["python3", "main.py"] ---> Running in 864440fa7988 Removing intermediate container 864440fa7988 ---> d6e31e5606b8 Successfully built d6e31e5606b8 Successfully tagged arg_py:latest
Step 3: Run the container
#docker run --name mycontainer arg_py HELLO FROM TUTORIALSPOINT
Example
File or Script Name is : main.py Arguments passed: HELLO FROM TUTORIALSPOINT hello from tutorialspoint
Using Docker environment variables with ENTRYPOINT
Docker run command provides us with some extraordinary functionalities, one of which is environment variables. Here we will use these environment variables to pass the data to the inside python script on the docker container.
Step 1: Create a python script for accessing the environment variable
This time creation of a python script will be very similar to the first example. Instead of importing the “sys” module, we will import the “os” module for fetching environment variables. Create a python file and paste the below code.
Example
import os #declare some variables for environment variable #os.getenv will fetch the environment variables from the container. userName = os.getenv("User_Name") passWord = os.getenv("Pass_Word") #Now print the variables that has been fetched. print("Running with user: %s" % userName) print("Your password: %s" % passWord) #Apply some operation print(userName.upper()) print(passWord.upper())
Save the above file as main.py
Step 2: Bulid the dockerfile
Build the dockerfile to create a new image with this python code. This dockerfile is the same that we created before only the python code in main.py is changed.
Example
#docker build -t env_img .
Output
Sending build context to Docker daemon 3.072kB Step 1/4 : FROM python ---> fa9122485d1d Step 2/4 : WORKDIR /app ---> Using cache ---> 9e9708fe1d43 Step 3/4 : COPY . /app/ ---> 31f98d53c161 Step 4/4 : ENTRYPOINT ["python3", "main.py"] ---> Running in bec1681a6842 Removing intermediate container bec1681a6842 ---> 5dd89b0c7985 Successfully built 5dd89b0c7985 Successfully tagged env_img:latest
Step 3: Run the container
Use the environment variables mentioned in the python script during running the container. Docker run has a ‘-e’ flag to mention any environment variable, we can mention multiple environment variables at a time
Example
#docker run -e User_Name="TutorialsPoint" -e Pass_Word="secret" --name env_cont env_img
Output
Running with user: TutorialsPoint Your password: secret TUTORIALSPOINT SECRET
This is how we can pass command line arguments and environment variables to the python container running on the docker daemon with the help of the docker client.
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