Argo CD is a popular GitOps tool for managing Kubernetes applications. While it appears simple to use, scaling GitOps practices effectively depends on the chosen architecture. This article explores three common architectures for implementing Argo CD:
1. Single Instance:
Advantages:
- Single view for deployment activity across all clusters.
- Single control plane, simplifying installation and maintenance.
- Single server for easy API/CLI integration.
Disadvantages:
- Scaling requires tuning of individual components.
- Single point of failure for deployments.
- Admin credentials for all clusters in one place.
- Requires a separate “management” cluster.
- Significant network traffic between Argo CD and clusters.
This architecture is popular for its simplicity and single view of applications. However, it has limitations regarding scalability, security, and network traffic.
Best for: Small environments with limited clusters and applications.
2. Instance Per Cluster:
Advantages:
- Distributes load per cluster.
- No direct external access is required.
- Eliminates Argo CD traffic leaving the cluster.
- An outage in one cluster won’t affect other clusters.
- Credentials are scoped per cluster.
Disadvantages:
- Requires maintaining multiple instances and duplicating configuration.
- At a particular scale, each instance could still require tuning.
- API/CLI integrations need to specify which instance.
- Negative developer experience
This architecture improves security and reduces network traffic but requires more maintenance and has a more complex developer experience.
Best for: Environments with many clusters per environment.
3. Instance Per Logical Group:
Advantages:
- Distributes load per group.
- An outage in one cluster won’t affect other groups.
- Credentials are scoped per group.
- Single view for deployment activity across a group.
- Configuration duplication is reduced.
- Easy to understand location for API/CLI integration.
Disadvantages:
- Requires maintaining multiple instances.
- At a certain scale, each instance could still require tuning.
- API/CLI integrations need to specify the right instance.
- Requires a separate “management” cluster.
This architecture balances the previous two, offering improved security, developer experience, and scalability.
Best for: Balancing the benefits of single and per-cluster architectures.
Choosing the Right Architecture:
The number of Argo CD instances you need depends on several factors:
- Size and complexity of your environment:
- If small and new to Kubernetes, a single instance may suffice. (<3 clusters, <100 applications)
- If larger and using a cluster per environment, per-cluster instances are common. (>3 clusters, >100 applications)
- Number of users and applications:
- More users and applications may require more instances.
- Workload:
- Higher workload may require more instances or scaling per cluster.
Conclusion:
Carefully consider these factors and your organization’s situation to choose the best architecture for your Argo CD implementation.
