Docker Compose vs. Docker Swarm: Differences & Use Cases

You need more than one tool to scale and manage Docker containers efficiently when building an application that has more than one service. Docker, Inc. the company that developed Docker containers, builds and maintains various container tools and platforms that streamline container processes. Docker Compose and Docker Swarm emerged as Docker’s most successful service management built-in tools.

Even though Docker, Inc. created the Docker Swarm, it no longer maintains it as actively as before. Swarm is now community-supported, and Kubernetes has largely replaced it as the preferred orchestrator

Docker Compose streamlines the process of creating and managing containers simultaneously. On the other hand, Docker Swarm orchestrates and scales container applications. In this article, you will learn the key differences between Docker Compose and Docker Swarm.

#What is the difference between Docker Compose and Docker Swarm?

Docker Compose is a tool that eliminates issues arising from managing different service configuration files simultaneously by using one file to define and configure multiple application services. On the other hand, Docker Swarm manages and scales container applications up and down to ensure they do not crash when traffic quadruples and reduce resource usage when traffic is very low.

#What is Docker Compose?

Before Docker Compose existed, developers had to pull images individually and configure services using multiple Docker commands. This container configuration workflow was tedious and cumbersome. The configuration error rate increases when defining multiple services using different configuration files. Docker Compose strives to reduce the error rate associated with managing multiple service configuration files.

Docker Compose uses one file, which is the docker-compose.yml to configure multiple application services. Managing one YAML configuration file that defines multiple services makes it easy to detect errors and misconfigurations. The docker-compose.yml allows you to define resources and components, such as

• Services
• Volumes
• Images
• Network ports
• Container specifications

The most critical capability that comes with docker-compose.yml is consistency in setting the version across different applications. Consistency in setting the version in a docker-compose.yml file is important because it guarantees that every application adheres to the same configuration syntax and capabilities.

All of the services, images, and volumes can be executed all at once using the docker-compose up command. This command will also start your application. The docker-compose up command can run services in the background when the --detach flag is executed.

To expand the number of containers and resources, use the --scale option. Using it, you can launch many container instances for the same service. For example, running docker-compose up --scale web=3 will launch three container instances for the web service, each operating concurrently. This allows you to distribute traffic across multiple containers and simulates production scenarios where horizontal scaling is critical.

Below is a code snippet from a docker-compose.yml file. The database service uses a MySQL database. The container_name: my_database sets a custom name for the container, making it easier to reference. The environment section enables you to add key-pair values that specify the database's name, users, and passwords. The ./data:/var/lib/mysql key-pair value maps a directory from the host to the container’s data directory, ensuring that the database data persists even if the container is removed.

services:
  database:
    image: mysql:5.7
    container_name: my_database
    environment:
      MYSQL_DATABASE: example_db
      MYSQL_USER: user
      MYSQL_PASSWORD: password
      MYSQL_ROOT_PASSWORD: rootpw
    volumes:
      - ./data:/var/lib/mysql
    ports:
      - "3306:3306"

The backend service shown in the below code snippet uses a local image which can be retrieved using the build context. The build: ./backend configuration allows you to instruct Docker to build an image using the Dockerfile located in the ./backend directory.

Since the backend service depends on the database service, it has to be declared in the docker-compose.yml. You can link the two services using the depends_on configuration setting. This will ensure that the backend service starts after the database service has been initiated.

 backend:
    build: ./backend
    container_name: my_backend
    depends_on:
      - database
    ports:
      - "5000:5000"

#Docker Compose use cases

Below are three Docker Compose use cases you should know.

• Prototyping and iterative development: Docker Compose strengthens efficient prototyping. You can easily change the configuration for multiple services with one YAML file. Making quick changes enables you to test and identify working and failing service configuration specifications easily.

• Local development and testing: Docker Compose simplifies the process of setting up complex development environments with databases, web servers, and other services. This ensures consistency across production and development environments. Every developer on your team can use the same configuration. Therefore ensuring that different environments are consistent and reducing the “it works on my machine” issues. It also facilitates running integration tests against the entire application stack.

• CI/CD pipeline integration: Docker compose fits perfectly into the DevOps workflow as it enables rapid application deployments and testing. These tasks can be automated when you integrate Docker Compose with a CI/CD tool.

  You can use CI/CD tools with Docker Compose to make the process of building and deploying container images automatic. You can set up a pipeline that uses commands like docker-compose up to quickly start up the whole application stack.

#What is Docker Swarm?

Docker Swarm is a built-in container orchestration and deployment management tool. It can be activated through the Docker Swarm mode. Docker Swarm is an alternative to Kubernetes. Its lightweight design uses fewer resources than Kubernetes. It is ideal for smaller clusters or simpler deployments. It also provides essential features for quick deployment and scaling of containerized applications.

Even though Docker Swarm is very simple to set up, many CTOs choose Kubernetes over Docker Swarm for its robust scalability mechanisms.

Docker Swarm works by joining and creating a cluster of Docker engines. The Docker engine is the underlying core that drives Docker processes. It consists of:

• Docker Daemon
• Docker CLI(Docker client)
• Container runtime
• REST API

A cluster of Docker engines utilizes multiple nodes that can be physical or virtual. These nodes are interconnected. A collection of interconnected nodes facilitated by a cluster of Docker daemons(Docker engine) is called a Swarm. And that's why the tool is called Docker Swarm. These nodes can be divided into two categories:

1. Manager nodes: Manager nodes are responsible for facilitating critical Docker swarm processes such as scheduling services and serving swarm mode HTTP endpoints. This facilitates operations like scaling services, updating configurations, and monitoring the cluster's health.

   Manager nodes are critical, you can’t execute worker nodes without a manager node. Manager nodes use consensus algorithms like Raft to maintain and replicate the swarm state. This built-in fault tolerance ensures that even if one manager node fails, the swarm remains operational.

2. Worker nodes are facilitated by manager nodes and are responsible for executing the container workload. Worker nodes also implement deployments and services. When you deploy an application or service, the manager nodes coordinate the rollout by scheduling tasks on the available worker nodes. This process distributes containers across the cluster to achieve the desired state. If a container fails or additional capacity is needed, the worker nodes adjust based on the manager nodes' configuration.

To enable load balancing, a service can have a port that makes it accessible to external load balancers. By default, all Swarm nodes implement a TLS authentication mechanism that secures communication between internal and external network traffic.

#Docker Swarm use cases

Below are Docker Swarm use cases you should know.

• Production deployments: Docker Swarm is designed to orchestrate containers in production environments. It provides features such as service discovery, load balancing, and rolling updates. This makes it suitable for deploying and managing applications at scale. \

• Scaling applications across multiple hosts: Swarm allows you to easily scale your application by adding or removing nodes to the swarm. It distributes containers across the cluster to maximize resource utilization and handle increased traffic. \

• Fault tolerance and disaster recovery: Swarm provides fault tolerance by replicating services across multiple nodes. If one node fails, the containers running on that node are automatically rescheduled on other healthy nodes. This helps to ensure high availability and resilience.

#Key differences between Docker Compose and Docker Swarm

Below is a list of factors that compare and differentiate Docker Swarm from Docker Compose.

#Deployment scope

Docker Compose: Docker Compose is suitable for development and testing but it is not suitable for multi-host clusters. It doesn't include the built-in mechanisms needed for managing containers across multiple hosts, which is why solutions like Docker Swarm are used for multi-host clusters. Docker Compose focuses on creating and defining YAML files that configure containers running on a single-host machine. This simplicity makes it ideal for setting up isolated development environments without the complexity of managing distributed systems.

Docker Swarm: Docker Swarm is built and designed to orchestrate containers running on multi-host containers. It is good for production tasks such as deploying applications and scaling them. In addition, Docker Swarm can handle extensive workloads and service failure through self-healing mechanisms such as automatic rescheduling of failed containers and node failure recovery.

#Service discovery and load balancing

Docker Compose relies on container linking and host-level port mapping. Even though it supports communication between containers, it does not have built-in load balancing across multiple instances. It does not have sophisticated load balancing and service discovery mechanisms. To be able to bypass and solve this issue, you need to integrate Docker Compose with external tools like NGINX's reverse proxy.

In contrast, Docker Swarm has built-in service discovery and load-balancing features. When a service is deployed in Swarm mode, an internal DNS service automatically distributes requests to the available container instances. This built-in load balancing improves performance and reliability, particularly for distributed scalable applications.

#CLI and workflow

The command-line interface and workflow differ between the two tools.

Developer-friendly CLI in Compose: Docker Compose provides a developer-friendly CLI with commands like

1. docker-compose up
2. docker-compose down
3. docker-compose ps

The workflow is straightforward, making it easy to define, manage, and run multi-container applications locally.

Production-grade commands in Swarm: Docker Swarm's CLI offers commands for managing the swarm, deploying services, scaling replicas, and performing other production-grade operations. The commands are more extensive and geared towards managing a distributed environment.

#Conclusion

In this article, you have learned what Docker Compose and Docker Swarm are in detail. In addition, you have learned different use cases for the two tools. Docker Swarm and Docker are a great combination for managing and facilitating containerized application tasks when using microservices. They are both good at their core purposes.

Docker Compose and Docker Swarm both handle different services at the same time. They are tools used in distributed services environments. These kinds of environments require specialized network solutions that distribute network requests among different services accordingly. Cherry Servers provides you with a load balancer service, which allows you to balance incoming HTTP requests across different web servers and services. Sign up today and find out how Cherry Servers can boost your microservices network architecture.