What is ArgoCD? | Harness Blog

Kubernetes has become the foundation of modern application delivery, but managing deployments in Kubernetes at scale remains a significant challenge. As teams adopt microservices, operate across multiple clusters, and deploy more frequently, traditional CI/CD approaches often break down. Scripts grow fragile, manual interventions increase, and visibility into what’s actually running in production becomes limited.

GitOps was created to solve these problems. It uses Git as the system of record for application and infrastructure configuration. This model works for Kubernetes with tools like Argo CD. Harness.io and other platforms build on GitOps by adding orchestration, governance, and enterprise-level control on top of tools like Argo CD. This helps organizations scale delivery safely.

What Is Argo CD?

Argo CD is a Kubernetes-native deployment tool designed specifically to implement GitOps workflows. Instead of treating deployment as a one-time action triggered by  pipelines, Argo CD treats deployment as a continuous process. It constantly checks whether the state defined in Git matches the state running in Kubernetes and takes action when it doesn’t.

At its core, Argo CD changes deployment from an imperative model ("run these steps to deploy") to a declarative model ("this is what the system should look like"). Git is the source of truth, and Kubernetes clusters are always up-to-date reflections of what is defined in Git.

Argo CD started as part of the Argo project and is now a graduated project of the Cloud Native Computing Foundation (CNCF). Its graduation means that it is mature, stable, and widely used in the Kubernetes ecosystem. Today, teams of all sizes, from small startups to large businesses with complicated, multi-cluster environments, use Argo CD.

Core Principles Behind Argo CD

The goal of Argo CD is to make GitOps principles part of everyday Kubernetes tasks. These rules explain how to handle configuration, how to make changes, and how to keep systems working over time.

Git as the Single Source of Truth

In Argo CD, all application configuration lives in Git repositories. This includes Kubernetes manifests, Helm charts, Kustomize overlays, and environment-specific configuration.

This method has a number of important benefits:

• Every change to a deployment is saved as a Git commit, which makes a permanent, unchangeable record.
• Git history also serves as deployment history, making audits and investigations easier.
• Rollbacks are easy, dependable, and can be undone by reverting commits.

By using Git to anchor deployments, teams can see and share ownership of changes to the system, instead of relying on tribal knowledge or scripts that aren't written down.

Declarative System Configuration

Argo CD enforces a declarative approach to application delivery. Instead of defining step-by-step deployment instructions, teams declare the desired state of their applications and environments.

Argo CD supports multiple declarative formats, including:

• Plain Kubernetes YAML for low-level control‍
• Helm charts for reusable, templated configuration
• Kustomize for environment-specific overlays and composition
• Jsonnet for advanced configuration logic

Declarative configuration makes deployments more predictable and less confusing. When something goes wrong, teams can look at Git to see how the system was supposed to work instead of trying to figure out how to deploy it after the fact.

Continuous Reconciliation

Argo CD's reliability is based on continuous reconciliation. Argo CD is always checking the live state in Kubernetes against the desired state stored in Git.

When differences appear, Argo CD:

• Detects and surfaces drift immediately
• Flags affected resources as out of sync
• Automatically takes corrective action or waits for approval, depending on the policy.

This continuous feedback loop stops silent configuration drift, speeds up the time it takes to recover, and makes sure that environments stay the same over time, even when there are manual changes or deployments that don't work.

Pull-Based Deployment Model

Argo CD uses a pull-based deployment model, which changes the way deployments work with Kubernetes clusters in a big way.

 This is how it works:

• Argo CD runs in or next to the cluster.
• It gets configuration straight from Git repositories.
• You don't need cluster credentials to use CI pipelines.

This separation lowers the risk to security, limits the number of credentials that are exposed, and makes access control easier. Many businesses use Argo CD with platforms like Harness to enforce governance and policy on a large scale because it also meets enterprise security needs.

How Argo CD Works (Step-by-Step)

Argo CD manages deployments through a continuous, automated reconciliation loop.

1. Developers define application configuration in Git using YAML, Helm, or Kustomize, committing changes through pull requests.
2. Argo CD continuously monitors the Git repository for updates or changes.
3. The application controller compares the desired state from Git with the live state of Kubernetes resources.
4. Any differences are identified as drift and surfaced in the Argo CD UI and CLI.
5. A synchronization process applies changes, either automatically or with manual approval.
6. Argo CD continuously reports application health, sync status, and history to operators.

This process ensures that deployments are not one-time events but ongoing, self-correcting workflows.

Argo CD Architecture & Key Components

Argo CD’s architecture is intentionally modular, so it can work with multiple teams and clusters while still being Kubernetes-native.

API Server

The API server exposes REST and gRPC interfaces that power:

• The Argo CD web UI
• The CLI used for automation and scripting
• External integrations and tooling

It also handles authentication and authorization, acting as the central access point for users and systems.

Application Controller

The application controller is the core reconciliation engine. It is responsible for:

• Continuously monitoring application state
• Detecting drift between desired and live resources
• Executing sync operations and remediation

Without the application controller, Argo CD would not be able to enforce Git-defined state.

Repository Server

The repository server manages all interactions with Git repositories. It:

• Fetches application configuration
• Renders manifests from Helm, Kustomize, or Jsonnet
• Supplies rendered manifests to the application controller

This separation improves performance and security, especially in large environments.

UI & CLI

Argo CD provides both a web-based UI and a CLI to support different workflows.

The UI offers:

• Real-time visibility into sync and health status
• Visual diffing of live vs desired state
• Easy troubleshooting and rollback workflows

The CLI enables automation, scripting, and integration into existing pipelines.

ApplicationSets & Projects

To support scale, Argo CD introduces Projects and ApplicationSets.

• Projects define logical boundaries, access controls, and allowed destinations
• Application Sets automate the creation and management of large numbers of applications across clusters and environments

These features are essential for organizations managing fleets of services and clusters.

Argo CD Features & Capabilities

Argo CD’s feature set is designed around operational clarity and control.

Key capabilities include:

• Real-time application status, health checks, and diffs
• Manual and automated synchronization strategies
• Native multi-cluster deployment support
• Fine-grained role-based access control
• Sync hooks and waves for ordered, complex rollouts
• First-class support for Helm, Kustomize, Jsonnet, and YAML

Together, these features make Argo CD suitable for both simple and highly complex deployment scenarios.

Why Use Argo CD? Benefits

‍As a GitOps deployment tool, Argo CD continuously monitors your running infrastructure (the actual state) to compare it to declaratively-defined code (the desired state or target state) to determine whether they are out of sync, which helps to remediate configuration drift. ‍

Argo CD automatically deploys new configurations and new version code to the target environment. Depending on how you’ve configured Argo CD to work, it’ll either notify you that things are out of sync after a new git commit, or take action. If you’ve set it up to automatically enforce changes, it’ll overwrite the production configuration with what’s stored in your immutable, versioned Git repository. The tool is great for complex application rollouts.‍

By automating lifecycle management and application deployment, Argo CD proactively monitors your application configuration for any potential syncing issues before it reaches your production environment.

Argo CD improves delivery outcomes by replacing manual processes with automated, declarative workflows.

Teams benefit from:

• Faster deployments with fewer human errors
• Clear, auditable change control through Git
• Early detection of unintended configuration changes
• Strong consistency across environments
• Improved visibility into deployment health and history

At scale, organizations often enhance these benefits by layering Harness.io on top of Argo CD to provide orchestration, governance, and cross-service visibility.

Common Argo CD Use Cases

Argo CD is commonly used in scenarios such as:

• Managing deployments across development, staging, and production environments
• Operating large, multi-cluster Kubernetes fleets‍
• Supporting microservices architectures with frequent releases
• Enabling platform engineering teams and internal developer platforms
• Meeting compliance requirements in regulated industries

Challenges & Considerations

Despite its strengths, Argo CD introduces new operational considerations.

Teams should plan for:

• The learning curve associated with GitOps and declarative workflows
• Secure and scalable secrets management
• Deciding between automatic and manual sync strategies
• Scaling RBAC, policy enforcement, and governance
• Connecting Argo CD deployments to the rest of the DevOps workflow (tests, scans, etc)
• Multi-cloud or multi-cluster deployment orchestration

Addressing these challenges early helps teams adopt Argo CD successfully.

Argo CD vs Other CI/CD Tools

Argo CD plays a distinct role in modern delivery pipelines.

• Compared to Jenkins and other CI tools, Argo CD focuses on deployment and reconciliation, not builds.‍
• Compared to Flux, Argo CD offers a richer UI and different scaling approaches.
• Compared to push-based CD tools, Argo CD’s pull-based model improves security and drift management but has weaker integration with testing and scanning tools.

Getting Started With Argo CD

To get started with Argo CD:

• Install Argo CD into a Kubernetes cluster
• Connect a Git repository containing application configuration
• Create an application resource and observe sync and health in the UI

From there, teams can incrementally scale adoption across environments and clusters.

Argo CD Frequently Asked Questions

What is Argo CD and how does it work?

Argo CD is an open-source GitOps continuous delivery tool designed for Kubernetes. It continuously monitors your Git repositories for declarative configuration changes and automatically syncs them with your Kubernetes clusters, ensuring that the desired state in Git matches the actual state in your environment.

How does Argo CD differ from other CI/CD tools?

Unlike traditional CI/CD tools that handle both integration and deployment, Argo CD specializes in the deployment aspect by focusing on GitOps principles. It automates the deployment process by managing Kubernetes configurations directly from Git repositories, providing real-time synchronization and version control. It lacks integrations across the SDLC that many CI/CD tools have.

What are the benefits of using Argo CD for Kubernetes deployments?

Argo CD offers several benefits, including automated synchronization of infrastructure, enhanced visibility into deployment pipelines through its user interface, support for complex application rollouts, and the ability to detect and remediate configuration drifts. This leads to faster, more reliable deployments and improved developer productivity.

What are the limitations of Argo CD?

While Argo CD excels in automating Kubernetes deployments, it has limitations in governance, such as limited role-based access control and a lack of comprehensive audit trails (some elements are in Git, and others are in each Argo controller). These challenges are most pronounced when operating many Argo instances and trying to standardize across them.

How can Harness enhance the functionality of Argo CD?

Harness GitOpsaddresses Argo CD’s limitations by providing enhanced governance, scalable multi-cluster management, and integrated quality checks. It also streamlines the integration to other parts of the SDLC. This integration ensures more stringent deployment processes, better security, and simplified management for enterprise organizations.

Is Argo CD suitable for enterprise-scale deployments?

Out of the box, Argo CD is ideal for automating Kubernetes deployments but may require additional tools and configurations to meet enterprise-scale needs. By leveraging Harness GitOps, organizations can achieve the scalability, governance, and reliability required for large-scale, complex deployments.

Is Argo CD the Right GitOps Tool for Your Kubernetes Strategy?

Argo CD has become a cornerstone of modern Kubernetes delivery by transforming Git into the deployment control plane. Through declarative configuration, continuous reconciliation, and a pull-based model, it enables teams to deploy faster while reducing operational risk.

For organizations running Kubernetes at scale, Harness extends Argo CD with enterprise-grade continuous delivery, orchestration, and governance, turning GitOps into a sustainable, production-ready strategy.

If you’re serious about operating Kubernetes reliably and efficiently, Argo CD is one of the most powerful tools you can adopt today.