How to capture the incoming and outgoing messages of a Docker container

Docker is a containerization technology that can be used to quickly deploy and run applications. However, during actual operation, we sometimes need to understand the incoming and outgoing messages of the Docker container to better monitor and manage the container.

This article will introduce how to capture the incoming and outgoing packets of the Docker container, including using tcpdump and Wireshark to capture packets.

1. Use tcpdump to capture packets

1. Install tcpdump

In the Linux system, use the following command to install tcpdump:

sudo apt-get install tcpdump

2. Find the ID of the target container

Use the following command to get the running container ID:

docker ps

3. Enter the container

Use the following command Enter the shell environment of the container:

docker exec -it <ContainerID> /bin/bash

where <ContainerID> is the ID of the target container.

4. Capture packets

Execute the following command in the container to capture incoming and outgoing packets:

tcpdump -i any -s 0 -w /tmp/docker.pcap

Among them, -i any means to monitor all network cards, -s 0 means to capture all data packets, and the -w parameter specifies to write the captured packets into the specified file. In the above command, we write incoming and outgoing packets into the /tmp/docker.pcap file.

5. Exit the container

Execute the following command in the container to exit the container:

exit

6. Copy the pcap file to the local

Use the following command to copy the /tmp/docker.pcap file in the container to the local:

docker cp <ContainerID>:/tmp/docker.pcap .

Where, <ContainerID> is the ID of the target container.

7. View messages

Use Wireshark to open the docker.pcap file to view the incoming and outgoing messages of the container.

2. Use Wireshark to capture packets

1. Install Wireshark

In the Linux system, use the following command to install Wireshark:

sudo apt-get install wireshark

2. Find the IP address of the target container

Use the following command to obtain the IP address of the running container:

docker inspect <ContainerID> | grep IPAddress

Among them, <ContainerID> is the target container ID.

3. Run Wireshark

Enter the following command in the terminal to start Wireshark:

sudo wireshark

After entering the Wireshark interface, select the network card that needs to be monitored, and then enter the following Filter:

ip.addr == <ContainerIP>

Among them, <ContainerIP> is the IP address of the target container.

4. Packet capture

Start capturing the incoming and outgoing packets of the container, and click the "Start Capturing" button in Wireshark.

5. View messages

You can view the incoming and outgoing messages of the container in Wireshark.

This article introduces the method of using tcpdump and Wireshark to capture the incoming and outgoing messages of the Docker container, which can help us better monitor and manage the Docker container. At the same time, it should be noted that packet capture may have certain risks and should be used with caution.

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