One of the most basic ways in which a project gets deployed is by SSHing into a remote host followed by executing a few basic commands. Apart from deployment, this can also be useful for running any command you want on a remote host, such as when a CI/CD pipeline is triggered. In this article I'll be taking a look on how to deploy a basic project to a remote server through Gitlab CI using Python Fabric. What is Fabric? is an open source python library that is used to execute commands remotely over SSH. Fabric Fabric is compatible with Python 2 and 3. To use it with Python3, install it with: pip3 install fabric Since the end goal here is to use fabric in an automated deployment pipeline, you don't actually need to have fabric installed on your local machine (unless that is where your pipeline runs). Installing fabric also installs the binary stub, which essentially allows fabric to read and execute commands defined in a file called the fabfile. fab Creating a fabfile Create a file named and start out with the following code: fabfile.py fabric task print( ) from import @task : def deploy (ctx) "Inside the task!" This defines a task called "deploy" which can be passed as an argument to the fab binary for execution. The decorator (Which is the Python equivalent of a closure - a subroutine that takes another subroutine as a parameter or returns another subroutine.) is used to convert the function to a task that can be executed by the fab binary. The function must take a context argument, which is given as in this case. @task deploy ctx On executing this by running from the same directory as , "Inside the task!" will be printed as the output. fab deploy fabfile.py Now to use this to do what Fabric is intended for - connecting a remote host and executing commands in it. fabric Connection, task Connection( ) c: c.cd( ):
            c.run( )
            c.run( )
            c.run( ) from import @task : def deploy (ctx) with "HOST" as with "/home/project/path/" "docker-compose down" "git pull origin master --recurse-submodules --rebase" "docker-compose up --build -d" Here, replace with the name or IP address of the host to which you are establishing a connection. From there, you can execute any command that the user as which you are logged in has permission to do. is used to ensure the remaining commands are executed from that particular folder. The commands I have given after this with are just examples. Replace them with what you need to execute. HOST c.cd() c.run() In this example I'm making use of Python context managers with the help of blocks, but there are many other ways to do this as well. You can read up on the to explore other ways to do this. with Fabric documentation By now you might have noticed just the host name is often not enough to establish a connection. What about the username and the private key to establish an SSH connection? This isn't immediately obvious, but because Fabric uses a library called under the hood for handling the SSH side of things, we can pass arguments to Paramiko's method by using the argument in Fabric's Connection. This looks like the following: Paramiko SSHclient.connect connect_kwargs fabric Connection, task Connection( ,
        user= ,
        connect_kwargs={ : }
    ) c: c.cd( ):
            c.run( )
            c.run( )
            c.run( ) from import @task : def deploy (ctx) with "HOST" "USERNAME" "key_filename" "~/.ssh/your_key" as with "/home/project/path/" "docker-compose down" "git pull origin master --recurse-submodules --rebase" "docker-compose up --build -d" Paramiko's takes a argument, which specifies the filename of the key to be used. Now you are passing all the info required to establish a connection via SSH. SSHclient.connect key_filename You can also pass the SSH key as an instance of Paramiko's class, or make use of a bunch of other options, which you can find in . pkey.Pkey Paramiko's documentation Of course, it's much safer to load all of these as environment variables. When using Gitlab CI, while setting the environment variables you can choose to make the key available as a file instead of a string, which is needed to make it work with the argument. key_filename Here is a screenshot of the Variables section under Gitlab CI/CD settings with the hostname added as a string and the key added as a file. You might want to load these values in other ways depending on how your team is organized and as per your security requirements. With these environment variables in place, the fabfile changes to this: os fabric Connection, task Connection(
        os.environ[ ],
        user= ,
        connect_kwargs={ : os.environ[ ]},
    ) c: c.cd( ):
            c.run( )
            c.run( )
            c.run( ) import from import @task : def deploy (ctx) with "HOST" "USERNAME" "key_filename" "DEPLOY_KEY_FILE" as with "/home/project/path/" "docker-compose down" "git pull origin master --recurse-submodules --rebase" "docker-compose up --build -d" Setting up Gitlab CI Now that the fabfile is ready, executing it with the Python Fabric package is all we have to do. This can be done in any way you want - manually, using Github actions, etc. Here I have an example of running it with Gitlab's CI. To do this, create a file at the project root. An example is given below: .gitlab-ci.yml image: "python:3.6" stages: - deploy deploy_to_production: stage: deploy script: - pip3 install fabric - fab deploy only: - master This is a basic configuration file that should be easy to understand if you're familiar with Gitlab's CI. It just has one job called that executes two things (It uses a Python 3 image as base): to install Fabric, and , which makes Fabric read our and execute the task named "deploy" in it. deploy_to_production pip3 install fabric fab deploy fabfile.py Conclusion Fabric has quite a lot more options than what is outlined here - such as dealing with sending the sudo password to the remote host when it's required, dealing with multiple hosts etc. It's worth going through their if you're planning to make use of it. documentation In conclusion, this is a really simple and effective way to programmatically build scripts to be executed over SSH and trigger them from common methods such as through a CI/CD tool. I hope you found this post useful. You can find me on and . Twitter LinkedIn

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