Run a Flask Container App

back4app containers is the perfect platform for hosting your flask applications with its ability to automatically deploy dockerized flask apps, you can effortlessly launch your project in a scalable and flexible environment in this comprehensive guide, we will walk you through the process of preparing and deploying your flask application on back4app containers, covering everything from simple projects to more complex setups if you have any questions or comments, feel free to join the conversation in the #containers channel on the back4app community on slack for discussions specific to flask on back4app containers anytime you can also contact us at community\@back4app com at anytime if you want to check a sample working flask project on back4app containers go to https //github com/templates back4app/containers python flask sample https //github com/templates back4app/containers python flask sample 1 prepare your flask application make sure your flask application is structured properly and that all necessary files, including templates and static files, are organized in the project directory for more complex projects, ensure that you have a proper app factory setup and follow flask best practices 2 create a requirements txt file list all required dependencies and their versions in a requirements txt file this file will be used by the dockerfile to install the necessary packages when building the docker image here's a sample requirements txt file for a flask application, including some common dependencies you might use in various projects feel free to add or remove packages as needed for your specific application requirements txt flask==2 1 1 gunicorn==20 1 0 werkzeug==2 1 1 jinja2==3 1 0 markupsafe==2 1 1 itsdangerous==2 1 1 click==8 1 2 sqlalchemy==1 4 29 flask sqlalchemy==2 5 1 flask migrate==3 1 1 flask login==0 5 0 flask wtf==1 0 3 wtforms==3 0 2 flask cors==3 1 1 flask mail==0 9 1 flask restful==0 3 9 flask script==2 0 6 requests==2 27 1 3 create a dockerfile write a dockerfile to define your application's docker image make sure to use a suitable base image (such as python 3 x slim ), install dependencies from the requirements txt file, copy your project files, expose the correct port, and specify the appropriate command to start your flask application (e g , using gunicorn ) example 1 basic flask application this dockerfile is for a simple flask application using gunicorn as the wsgi server dockerfilecopy code# base image from python 3 9 slim \# working directory workdir /app \# copy requirements file and install dependencies copy requirements txt requirements txt run pip install no cache dir r requirements txt \# copy the rest of the project files copy \# expose the server port expose 8080 \# command to start the server cmd \["gunicorn", " b", "0 0 0 0 8080", "app\ app"] example 2 flask application with waitress (alternative wsgi server) this dockerfile uses waitress, an alternative wsgi server that is suitable for production environments and can be used instead of gunicorn dockerfilecopy code# base image from python 3 9 slim \# working directory workdir /app \# copy requirements file and install dependencies copy requirements txt requirements txt run pip install no cache dir r requirements txt \# copy the rest of the project files copy \# expose the server port expose 8080 \# command to start the server cmd \["waitress serve", " host=0 0 0 0", " port=8080", "app\ app"] make sure to add waitress to your requirements txt file example 3 flask application with gunicorn and worker optimization this dockerfile uses gunicorn with worker optimization for better performance it adjusts the number of gunicorn worker processes based on the available cpu cores dockerfilecopy code# base image from python 3 9 slim \# install build dependencies and curl run apt get update && apt get install y no install recommends \\ build essential \\ curl \\ && rm rf /var/lib/apt/lists/ \# working directory workdir /app \# copy requirements file and install dependencies copy requirements txt requirements txt run pip install no cache dir r requirements txt \# copy the rest of the project files copy \# expose the server port expose 8080 \# calculate the number of worker processes based on the number of cpu cores cmd \["sh", " c", "gunicorn b 0 0 0 0 8080 workers $(($(nproc all) 2 + 1)) app\ app"] 4 test your application locally build and run the docker image locally to ensure that your flask application works as expected address any issues or errors before deploying to back4app containers docker build t your app name docker run p 8080 8080 your app name 5 push your project to a git repository create a gitignore file to exclude unnecessary or sensitive files from your repository (e g , pycache , env , pyc , etc ) initialize a git repository, commit your project files, and push them to a remote repository (e g , on github) 6 deploy your application on back4app containers after creating your back4app account you can follow the steps listed on the docs 1 connect you github repo with back4app 2 prepare your project for deployment in summary containers will follow the instructions detailed on your dockerfile and start to create your app 7 monitor deployment keep an eye on the deployment logs and status on the back4app containers dashboard address any errors or issues that arise during deployment in case of more complex projects, ensure that all necessary services (such as databases or external apis) are correctly configured and accessible notice that you also have a section called logs which lists all the running logs for your app and its also important to keep an eye on it to check if you have any problem with your app 8 troubleshooting common deployments errors are listed here other possible common errors when deploying flask applications are incorrect host configuration flask applications should be configured to run on host 0 0 0 0 when deployed on back4app containers if your application is using localhost or 127 0 0 1, it might not be accessible externally incompatible or missing dependencies ensure that all required dependencies are listed in your requirements txt file and that their versions are compatible with each other and your application code missing or incompatible dependencies can lead to runtime errors database connection issues if your flask application relies on a database, ensure that the connection string and credentials are correctly set up in the application configuration also, verify that the database is reachable from the back4app containers environment application crashes or unhandled exceptions unhandled exceptions or crashes in your flask application code can cause deployment failures or unexpected behavior examine your application logs for any error messages, and address any issues in your code incorrectly configured wsgi server make sure that your wsgi server (e g , gunicorn or waitress) is correctly configured in your dockerfile and that it starts your flask application using the right entry point (e g , app\ app) invalid environment variables or configuration check if your application relies on specific environment variables or configuration files, and ensure they are correctly set up in the back4app containers environment 8 scale your application for more complex projects that require additional resources or horizontal/vertical scaling, consider upgrading your back4app containers plan to handle increased traffic and load 9 sample application for a sample flask application project you can go to https //github com/templates back4app/containers python flask sample https //github com/templates back4app/containers python flask sample