CircleCI vs. Jenkins

CircleCI and Jenkins are two of the best-known tools for continuous integration and deployment.

Despite their age, they remain effective tools for helping your organization deploy faster and more reliably. They have many similarities and differences. These can be mundane, such as the placement of certain UI elements, or crucial to your business, such as cost and available plugins.

Jenkins provides extensive plugin support and is ideal for on-premises environments requiring flexibility. However, its complexity and need for infrastructure management can be drawbacks. CircleCI simplifies CI/CD with a managed environment, built-in caching, and better cloud integration, making it more efficient for teams and prioritizing ease of use and scalability.

Let’s take a closer look at both of them and discuss their similarities and differences.

What is Jenkins?

Jenkins is an open-source automation server used for software continuous integration and delivery. It automates various tasks, such as building, testing, and deploying applications.  It is easily extendable due to its vast ecosystem of plugins, making it easy to integrate into version control systems like Git, build tools like Maven/Gradle, and deployment platforms like AWS and Docker. 

Jenkins has a distributed architecture, making it easy to distribute workloads across multiple machines, speeding up the execution of jobs. This feature is useful for large projects that are heavily tested and deployed.

Jenkins emerged in 2011 as a self-hosted application. AWS EC2 wasn't even available until 2008, and by then, Jenkins' predecessor, "Hudson," was already well-established and deployed widely. Other services, such as JFrog, provide a managed Jenkins environment, and you'll usually find Jenkins installed on bare metal servers, VMs, cloud instances, and containers. The setup is fairly straightforward for all these methods, but management complexity varies depending on the deployment size. 

A single Jenkins host is effortless to manage, but things can get unwieldy once you start creeping into double and triple digits. You can see the complexity of managing Jenkins at scale in their docs.

Jenkins features

• Pipeline as code - Jenkins enables automation and version control through the definition of build and deployment workflows with code.
• Extensibility - It supports thousands of plugins that integrate with various tools, enhancing functionality for CI/CD, testing, and monitoring.
• Distributed builds - Jenkins enables workload distribution across multiple nodes, improving performance and parallel execution.
• Automated testing - It integrates with testing frameworks to automate and validate software quality at every stage of development.
• Security management - Jenkins offers role-based access control, credential storage, and integration with authentication systems for secure operations.

What is CircleCI?

CircleCI is a CI/CD platform that automates the process of building, testing, and deploying software. It helps developers integrate code changes more frequently and efficiently, ensuring that software development teams can detect and fix errors quickly.

It integrates with GitHub, Bitbucket, and GitLab, enabling automatic builds whenever changes are pushed to a repository. CircleCI supports Docker, Kubernetes, and various programming languages, making it flexible for different development environments.

Compared with Jenkins, CircleCI offers a cloud-based, managed solution, reducing the need for manual server maintenance. It also supports parallel job execution and caching, which speeds up development cycles.

CircleCI features

• Cloud-native and on-prem support - CircleCI offers cloud-hosted and self-hosted options for flexible CI/CD deployment.
• Orbs (reusable configurations) - Pre-packaged YAML configurations simplify integrations with third-party tools and reduce setup time.
• Parallelism and caching - It optimizes build performance with parallel job execution and dependency caching.
• Advanced Docker support - CircleCI natively supports Docker, allowing efficient containerized build and test workflows.
• Context-based security - Securely manages environment variables and secrets for controlled access across pipelines.

What are the differences between CircleCI and Jenkins?

Unlike Jenkins, CircleCI is a software-as-a-service-first solution for continuous integration and delivery. They offer similar capabilities. CircleCI offers a self-managed version, but the considerations involved are similar to those involved with Jenkins, so we'll focus on the SaaS version.

Like any SaaS product, infrastructure, scaling, and resilience management concerns are practically non-existent. CircleCI can experience outages; they have promised to reduce those.

Overall, if you aren't concerned about the number of 9s of uptime your deployment solution has, CircleCI is definitely the more straightforward solution to manage. Because Jenkins is self-hosted, you will have to resolve any downtime issues without any external help.

Let's take a closer look at the two tools.

1. Configuration files

Self-hosted vs. SaaS is a complicated debate, but both have pros and cons. The real concerns about these solutions involve their actual usage. Practitioners have personal preferences regarding both solutions. 

Overall, sentiment leans towards CircleCI due to its YAML-based configuration file. Jenkins' Groovy syntax is very powerful, but it's also proprietary. You are unlikely to find many native methods for Groovy in your favorite programming language. Let's look at each: 

With Jenkins, you can configure both declarative and scripted pipelines. The difference between them is that you cannot inject code directly into declarative pipelines (those that start with the word pipeline), whereas you can in scripted ones (those that start with the word node).

Declarative pipelines may seem limiting, but they are not. They allow you to access environment variables, add conditional logic to the statements, and easily add error handling and logging.

Let's look at a Jenkins declarative pipeline:

Jenkins

pipeline {
    agent any

    stages {
        stage('Build') {
            steps {
                echo 'Building the application...'
                // Add your build commands here
            }
        }

        stage('Test') {
            steps {
                echo 'Running tests...'
                // Add your test commands here
            }
        }

        stage('Deploy') {
            steps {
                echo 'Deploying the application...'
                // Add your deployment commands here
            }
        }
    }
}

CircleCI

version: 2.1

jobs:
  build:
    docker:
      - image: <your-build-image>
    steps:
      - checkout
      - run:
          name: Build the application
          command: |
            echo 'Building the application...'
            # Add your build commands here

  test:
    docker:
      - image: <your-test-image>
    steps:
      - checkout
      - run:
          name: Run tests
          command: |
            echo 'Running tests...'
            # Add your test commands here

  deploy:
    docker:
      - image: <your-deployment-image>
    steps:
      - checkout
      - run:
          name: Deploy the application
          command: |
            echo 'Deploying the application...'
            # Add your deployment commands here

workflows:
  version: 2
  build-test-deploy:
    jobs:
      - build
      - test:
          requires:
            - build
      - deploy:
          requires:
            - test

The content of the two files is similar despite the syntax differences. A significant benefit of using YAML is the native tools available in many programming languages if you need to generate these files dynamically. YAML will be more verbose, but Groovy can get a little complicated. Many engineers lament having to learn Groovy, but those who know it can create very powerful deployment scripts.

Overall, either one should be accessible to a seasoned engineer and should not be a significant hindrance.

2. User interface

Jenkins and CircleCI have similar user interfaces. However, Jenkins can feel dated and reminiscent of Web 1.0  despite attempts to enhance its appearance (e.g., the BlueOcean plugin), whereas CircleCI has a more modern feel.

The functional differences are undeniable if sometimes subtle. Developer sentiment will typically lean toward CircleCI unless the developer has extensive experience with Jenkins.

Overall, you will probably visit the UI less than the command line, except when monitoring your deployments.

Jenkins

CircleCI

3. Plugins and extensibility

CircleCI and Jenkins both support most of the tools you'll use in a typical deployment, including Git providers, cloud providers, container orchestration systems, build systems, etc. The major difference is that Jenkins supports far more tools than CircleCI does.

Jenkins has direct access to SSH, so it will allow you to run a complicated bash script to perform a crazy hack to keep a server going. For this reason, I typically call Jenkins the sledgehammer of CI tools.

Unfortunately, Jenkins's power can lead to massive security and reliability concerns. If an engineer has admin access to Jenkins, they can potentially do anything, including take down your production systems.

This is why it is really important to ensure proper access management, as the same engineer can even destroy the whole Jenkins installation. CircleCI is also very powerful, but its guardrails are a little easier to control because you don't have nearly the security footprint to manage.

The SaaS version is separated from your production environment, so building the controls necessary to prevent disaster is much easier. 

4. Pricing

Jenkins's major attraction is that it's free. If you aren't managing it at scale, the CapEx and OpEx involved are minimal. It can be run as a container on a Kubernetes cluster and is largely hands-off.

Jenkins may win on price, but when a company introduces massive scale and resilience concerns, its self-hosted deployment method and cost can quickly lose their luster. 

CircleCI offers four pricing levels, including a free tier that covers five users and up to 6000 build minutes.

5. Infrastructure deployments

Jenkins and CircleCI are excellent deployment tools for application code, but they aren't necessarily the best options for deploying infrastructure. Neither quite meets the requirements for self-service environments, drift detection, Terraform state management, and more.

Sure, you can bolt products together, but that involves considerable engineering time and risks a much larger footprint than a purpose-built solution like Spacelift. 

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Is CircleCI better than Jenkins?

If you are looking for a SaaS product that is easy to set up and configure, uses a modern language (YAML) for declaring pipeline workflows, and offers a strong integration ecosystem, CircleCI is better.

For organizations needing extensive customization and control, Jenkins remains a strong choice --- especially if you want something free (pay just for the infrastructure underneath it), highly customizable, with an extensive plugin ecosystem, and 100% self-managed.

The choice between CircleCI and Jenkins will also depend on your tool familiarity, your project's specific needs, the required level of control, and, of course, your infrastructure preferences. Whenever you are choosing a software tool, it is best to evaluate your options with trials before deciding which one best meets your needs.

Among the many popular alternatives to Jenkins, good alternatives are GitHub Actions, GitLab CI/CD, TravisCI, and Azure Pipelines.

Alternative to CircleCI and Jenkins - Spacelift

When it comes to infrastructure orchestration, generic CI/CD platforms such as CircleCI and Jenkins are not specialized enough to manage everything you might need in your workflows. That's where Spacelift shines.

With Spacelift, you get:

• Policies to control what kind of resources engineers can create, what parameters they can have, how many approvals you need for a run, what kind of task you execute, what happens when a pull request is open, and where to send your notifications
• Stack dependencies to build multi-infrastructure automation workflows with dependencies, having the ability to build a workflow that, for example, generates your ec2 instances using Terraform and combines it with Ansible to configure them
• Self-service infrastructure via Blueprints, or Spacelift's Kubernetes operator, enabling your developers to do what matters -- developing application code while not sacrificing control
• Creature comforts such as contexts (reusable containers for your environment variables, files, and hooks), and the ability to run arbitrary code
• Drift detection and optional remediation

If you want to learn more about what you can do with Spacelift, check out this article.

Key points

CircleCI is a cloud-based CI/CD platform that emphasizes ease of use, scalability, and quick setup, whereas Jenkins is an open-source, self-hosted tool offering extensive flexibility and customization but requiring more manual configuration and maintenance. CircleCI is often preferred for its simplicity, whereas Jenkins suits teams needing extensive control over their CI/CD pipelines.

With Spacelift, you have all the tools necessary to deploy your IaC without the bloat of app deployment build tools. So check it out today for a free trial and a custom-tailored personal demo!

Written by Derek Morgan and Flavius Dinu