How to copy Docker images from one host to another without using a repository

In the world of Docker, moving images from one host to another without a central repository is a common challenge. While many developers rely on docker save and docker load commands, there are other efficient methods to transfer Docker images directly between two hosts, using tools like netcat (nc) and ssh. Let’s dive into an alternative method that showcases how to leverage the power of netcat for quick and direct image transfers.

The Netcat Approach: Fast and Direct Image Transfers

Netcat is a versatile networking tool used for reading from and writing to network connections using TCP or UDP. It’s light, easy to use, and available by default on many Unix-like systems, making it an ideal choice for quick tasks like transferring Docker images. Here’s a step-by-step guide on how to use netcat for transferring a Docker image from one host to another:

1. On the Receiving Host:
   Start by setting up netcat to listen on a specific port and write the incoming data to a file. Choose a port that is open and not in use on your network.

   nc -l 12345 > ubuntu_image.tar
   

   Here, nc -l 12345 commands netcat to listen on port 12345, and > ubuntu_image.tar directs the incoming data stream into a file named ubuntu_image.tar.

2. On the Sending Host:
   After saving the Docker image into a tar file using docker save, you can then send this file directly to the receiving host using netcat.

   docker save ubuntu:latest | nc receiving_host_ip 12345
   

   This command pipes the output of docker save directly to netcat, which then sends it to the receiving host IP on port 12345.

3. On the Receiving Host:
   Once the transfer is complete, you can load the Docker image from the tar file into Docker:

   docker load -i ubuntu_image.tar
   

   This loads the image from the tar file into Docker, making it available for use.

Advantages of Using Netcat:

• Speed: Netcat doesn’t have the overhead of encryption like ssh, making transfers potentially faster over local networks.
• Simplicity: The process is straightforward without any need for intermediate storage or third-party services.
• Direct Transfer: Images are transferred directly from one host to another, which can be ideal for isolated networks or quick setups.

Considerations:

• Security: Since netcat does not encrypt traffic, it is best used within secure or isolated networks.
• Firewall Settings: Ensure that the ports used are open on both the sending and receiving hosts’ firewalls.

While docker save and load are the standard for moving Docker images without a repository, exploring tools like netcat provides a faster alternative for environments where security is not a concern, or the network is isolated. This method simplifies the process of Docker image transfer, making it efficient for developers working in dynamic environments where speed is crucial.