4 posts tagged with "network"

Overview​

Implementing a server application that can handle multiple client requests simultaneously is now very easy. Just using Spring MVC alone can get you there in no time. However, as an engineer, I am curious about the underlying principles. In this article, we will embark on a journey to reflect on the considerations that were made to implement a multi-connection server by questioning the things that may seem obvious.

Socket​

The first destination is 'Socket'. From a network programming perspective, a socket is a communication endpoint used like a file to exchange data over a network. The description 'used like a file' is important because it is accessed through a file descriptor (fd) and supports I/O operations similar to files.

To implement a server application using sockets, you need to go through the following steps:

What are Network Packets?​

How do we transmit data over a network? Establishing a connection with the recipient and sending the data all at once might seem like the most straightforward approach. However, this method becomes inefficient when handling multiple requests because a single connection can only maintain one data transfer at a time. If a connection is prolonged due to a large data transfer, other data will have to wait.

To efficiently handle the data transmission process, networks divide data into multiple pieces and require the receiving end to reassemble them. These fragmented data structures are called packets. Packets include additional information to allow the receiving end to reassemble the data in the correct order.

While transmitting data in multiple packets enables efficient processing of many requests through packet switching, it can also lead to various errors such as data loss or incorrect delivery order. How should we debug such issues? 🤔

Overview​

How many concurrent users can a Spring MVC web application accommodate? 🤔

To estimate the approximate number of users a server needs to handle to provide stable service while accommodating many users, this article explores changes in network traffic focusing on Spring MVC's Tomcat configuration.

For the sake of convenience, the following text will be written in a conversational tone 🙏

Overview​

Since Docker containers run in isolated environments, they cannot communicate with each other by default. However, connecting multiple containers to a single Docker network enables them to communicate. In this article, we will explore how to configure networks for communication between different containers.

Types of Networks​

Docker networks support various types of network drivers such as bridge, host, and overlay based on their purposes.

• bridge: Allows multiple containers within a single host to communicate with each other.
• host: Used to run containers in the same network as the host computer.
• overlay: Used for networking between containers running on multiple hosts.

Creating a Network​

Let's create a new Docker network using the docker network create command.

docker network create my-net

The newly added network can be verified using the docker network ls command, which confirms that it was created as a default bridge network since the -d option was not specified.

Network Details​

Let's inspect the details of the newly added network using the docker network inspect command.

docker network inspect my-net
[
    {
        "Name": "my-net",
        "Id": "05f28107caa4fc699ea71c07a0cb7a17f6be8ee65f6001ed549da137e555b648",
        "Created": "2022-08-02T09:05:20.250288712Z",
        "Scope": "local",
        "Driver": "bridge",
        "EnableIPv6": false,
        "IPAM": {
            "Driver": "default",
            "Options": {},
            "Config": [
                {
                    "Subnet": "172.18.0.0/16",
                    "Gateway": "172.18.0.1"
                }
            ]
        },
        "Internal": false,
        "Attachable": false,
        "Ingress": false,
        "ConfigFrom": {
            "Network": ""
        },
        "ConfigOnly": false,
        "Containers": {},
        "Options": {},
        "Labels": {}
    }
]

By checking the Containers section, we can see that no containers are connected to this network.

Connecting Containers to the Network​

Let's first run a container named one.

docker run -it -d --name one busybox
# af588368c67b8a273cf63a330ee5191838f261de1f3e455de39352e0e95deac4

If the --network option is not specified when running a container, it will by default connect to the bridge network.

docker network inspect bridge
#...
        "Containers": {
            "af588368c67b8a273cf63a330ee5191838f261de1f3e455de39352e0e95deac4": {
                "Name": "one",
                "EndpointID": "44a4a022cc0f5fb30e53f0499306db836fe64da15631f2abf68ebc74754d9750",
                "MacAddress": "02:42:ac:11:00:02",
                "IPv4Address": "172.17.0.2/16",
                "IPv6Address": ""
            }
        },
#...
]

Now, let's connect the one container to the my-net network using the docker network connect command.

docker network connect my-net one

Upon rechecking the details of the my-net network, we can see that the one container has been added to the Containers section with the IP 172.18.0.2.

docker network inspect my-net
[
    {
        "Name": "my-net",
        "Id": "05f28107caa4fc699ea71c07a0cb7a17f6be8ee65f6001ed549da137e555b648",
        "Created": "2022-08-02T09:05:20.250288712Z",
        "Scope": "local",
        "Driver": "bridge",
        "EnableIPv6": false,
        "IPAM": {
            "Driver": "default",
            "Options": {},
            "Config": [
                {
                    "Subnet": "172.18.0.0/16",
                    "Gateway": "172.18.0.1"
                }
            ]
        },
        "Internal": false,
        "Attachable": false,
        "Ingress": false,
        "ConfigFrom": {
            "Network": ""
        },
        "ConfigOnly": false,
        "Containers": {
            "af588368c67b8a273cf63a330ee5191838f261de1f3e455de39352e0e95deac4": {
                "Name": "one",
                "EndpointID": "ac85884c9058767b037b88102fe6c35fb65ebf91135fbce8df24a173b0defcaa",
                "MacAddress": "02:42:ac:12:00:02",
                "IPv4Address": "172.18.0.2/16",
                "IPv6Address": ""
            }
        },
        "Options": {},
        "Labels": {}
    }
]

Disconnecting a Container from the Network​

A container can be connected to multiple networks simultaneously. Since the one container was initially connected to the bridge network, it is currently connected to both the my-net and bridge networks.

Let's disconnect the one container from the bridge network using the docker network disconnect command.

docker network disconnect bridge one

Connecting a Second Container​

Let's connect another container named two to the my-net network.

This time, let's specify the network to connect to while running the container using the --network option.

docker run -it -d --name two --network my-net busybox
# b1509c6fcdf8b2f0860902f204115017c3e2cc074810b330921c96e88ffb408e

Upon inspecting the details of the my-net network, we can see that the two container has been assigned the IP 172.18.0.3 and connected.

docker network inspect my-net
[
    {
        "Name": "my-net",
        "Id": "05f28107caa4fc699ea71c07a0cb7a17f6be8ee65f6001ed549da137e555b648",
        "Created": "2022-08-02T09:05:20.250288712Z",
        "Scope": "local",
        "Driver": "bridge",
        "EnableIPv6": false,
        "IPAM": {
            "Driver": "default",
            "Options": {},
            "Config": [
                {
                    "Subnet": "172.18.0.0/16",
                    "Gateway": "172.18.0.1"
                }
            ]
        },
        "Internal": false,
        "Attachable": false,
        "Ingress": false,
        "ConfigFrom": {
            "Network": ""
        },
        "ConfigOnly": false,
        "Containers": {
            "af588368c67b8a273cf63a330ee5191838f261de1f3e455de39352e0e95deac4": {
                "Name": "one",
                "EndpointID": "ac85884c9058767b037b88102fe6c35fb65ebf91135fbce8df24a173b0defcaa",
                "MacAddress": "02:42:ac:12:00:02",
                "IPv4Address": "172.18.0.2/16",
                "IPv6Address": ""
            },
            "b1509c6fcdf8b2f0860902f204115017c3e2cc074810b330921c96e88ffb408e": {
                "Name": "two",
                "EndpointID": "f6e40a7e06300dfad1f7f176af9e3ede26ef9394cb542647abcd4502d60c4ff9",
                "MacAddress": "02:42:ac:12:00:03",
                "IPv4Address": "172.18.0.3/16",
                "IPv6Address": ""
            }
        },
        "Options": {},
        "Labels": {}
    }
]

Container Networking​

Let's test if the two containers can communicate with each other over the network.

First, let's use the ping command from the one container to ping the two container. Container names can be used as hostnames.

docker exec one ping two
# PING two (172.18.0.3): 56 data bytes
# 64 bytes from 172.18.0.3: seq=0 ttl=64 time=0.114 ms
# 64 bytes from 172.18.0.3: seq=1 ttl=64 time=0.915 ms

Next, let's ping the one container from the two container.

docker exec two ping one
# PING one (172.18.0.2): 56 data bytes
# 64 bytes from 172.18.0.2: seq=0 ttl=64 time=0.108 ms
# 64 bytes from 172.18.0.2: seq=1 ttl=64 time=0.734 ms
# 64 bytes from 172.18.0.2: seq=2 ttl=64 time=0.270 ms
# 64 bytes from 172.18.0.2: seq=3 ttl=64 time=0.353 ms
# 64 bytes from 172.18.0.2: seq=4 ttl=64 time=0.371 ms

Both containers can communicate smoothly.

Removing the Network​

Finally, let's remove the my-net network using the docker network rm command.

docker network rm my-net
# Error response from daemon: error while removing network: network my-net id 05f28107caa4fc699ea71c07a0cb7a17f6be8ee65f6001ed549da137e555b648 has active endpoints

If there are active containers running on the network you are trying to remove, it will not be deleted.

In such cases, you need to stop all containers connected to that network before deleting the network.

docker stop one two
# one
# two
docker network rm my-net
# my-net

Network Cleanup​

When running multiple containers on a host, you may end up with networks that have no containers connected to them. In such cases, you can use the docker network prune command to remove all unnecessary networks at once.

docker network prune
WARNING! This will remove all custom networks not used by at least one container.
Are you sure you want to continue? [y/N] y

Conclusion​

In this article, we explored various docker network commands:

• ls
• create
• connect
• disconnect
• inspect
• rm
• prune

Understanding networks is essential when working with Docker containers, whether for containerizing databases or implementing container clustering. It is crucial to have a good grasp of networking as a key skill for managing multiple containers effectively.

Reference​

• Docker Docs - Network
• Docker Network Usage