High Availability

Argo CD is largely stateless. All data is persisted as Kubernetes objects, which in turn is stored in Kubernetes’ etcd. Redis is only used as a throw-away cache and can be lost. When lost, it will be rebuilt without loss of service.

A set of HA manifests are provided for users who wish to run Argo CD in a highly available manner. This runs more containers, and runs Redis in HA mode.

NOTE: The HA installation will require at least three different nodes due to pod anti-affinity roles in the specs. Additionally, IPv6 only clusters are not supported.

Scaling Up

argocd-repo-server

settings:

The argocd-repo-server is responsible for cloning Git repository, keeping it up to date and generating manifests using the appropriate tool.

  • argocd-repo-server fork/exec config management tool to generate manifests. The fork can fail due to lack of memory or limit on the number of OS threads. The --parallelismlimit flag controls how many manifests generations are running concurrently and helps avoid OOM kills.

  • the argocd-repo-server ensures that repository is in the clean state during the manifest generation using config management tools such as Kustomize, Helm or custom plugin. As a result Git repositories with multiple applications might affect repository server performance. Read Monorepo Scaling Considerations for more information.

  • argocd-repo-server clones the repository into /tmp (or the path specified in the TMPDIR env variable). The Pod might run out of disk space if it has too many repositories or if the repositories have a lot of files. To avoid this problem mount a persistent volume.

  • argocd-repo-server uses git ls-remote to resolve ambiguous revisions such as HEAD, a branch or a tag name. This operation happens frequently and might fail. To avoid failed syncs use the ARGOCD_GIT_ATTEMPTS_COUNT environment variable to retry failed requests.

  • argocd-repo-server Every 3m (by default) Argo CD checks for changes to the app manifests. Argo CD assumes by default that manifests only change when the repo changes, so it caches the generated manifests (for 24h by default). With Kustomize remote bases, or Helm patch releases, the manifests can change even though the repo has not changed. By reducing the cache time, you can get the changes without waiting for 24h. Use --repo-cache-expiration duration, and we’d suggest in low volume environments you try ‘1h’. Bear in mind that this will negate the benefits of caching if set too low.

  • argocd-repo-server executes config management tools such as helm or kustomize and enforces a 90 second timeout. This timeout can be changed by using the ARGOCD_EXEC_TIMEOUT env variable. The value should be in the Go time duration string format, for example, 2m30s.

metrics:

  • argocd_git_request_total - Number of git requests. This metric provides two tags: repo - Git repo URL; request_type - ls-remote or fetch.

  • ARGOCD_ENABLE_GRPC_TIME_HISTOGRAM - Is an environment variable that enables collecting RPC performance metrics. Enable it if you need to troubleshoot performance issues. Note: This metric is expensive to both query and store!

argocd-application-controller

settings:

The argocd-application-controller uses argocd-repo-server to get generated manifests and Kubernetes API server to get the actual cluster state.

  • each controller replica uses two separate queues to process application reconciliation (milliseconds) and app syncing (seconds). The number of queue processors for each queue is controlled by --status-processors (20 by default) and --operation-processors (10 by default) flags. Increase the number of processors if your Argo CD instance manages too many applications. For 1000 application we use 50 for --status-processors and 25 for --operation-processors

  • The manifest generation typically takes the most time during reconciliation. The duration of manifest generation is limited to make sure the controller refresh queue does not overflow. The app reconciliation fails with Context deadline exceeded error if the manifest generation is taking too much time. As a workaround increase the value of --repo-server-timeout-seconds and consider scaling up the argocd-repo-server deployment.

  • The controller uses Kubernetes watch APIs to maintain a lightweight Kubernetes cluster cache. This allows avoiding querying Kubernetes during app reconciliation and significantly improves performance. For performance reasons the controller monitors and caches only the preferred versions of a resource. During reconciliation, the controller might have to convert cached resources from the preferred version into a version of the resource stored in Git. If kubectl convert fails because the conversion is not supported then the controller falls back to Kubernetes API query which slows down reconciliation. In this case, we advise to use the preferred resource version in Git.

  • The controller polls Git every 3m by default. You can change this duration using the timeout.reconciliation setting in the argocd-cm ConfigMap. The value of timeout.reconciliation is a duration string e.g 60s, 1m, 1h or 1d.

  • If the controller is managing too many clusters and uses too much memory then you can shard clusters across multiple controller replicas. To enable sharding increase the number of replicas in argocd-application-controller StatefulSet and repeat the number of replicas in the ARGOCD_CONTROLLER_REPLICAS environment variable. The strategic merge patch below demonstrates changes required to configure two controller replicas.

  1. apiVersion: apps/v1
  2. kind: StatefulSet
  3. metadata:
  4.   name: argocd-application-controller
  5. spec:
  6.   replicas: 2
  7.   template:
  8.     spec:
  9.       containers:
  10.       - name: argocd-application-controller
  11.         env:
  12.         - name: ARGOCD_CONTROLLER_REPLICAS
  13.           value: "2"
  • The shard distribution algorithm of the argocd-application-controller can be set by using the --sharding-method parameter. Supported sharding methods are : [legacy (default), round-robin]. legacy mode uses an uid based distribution (non-uniform). round-robin uses an equal distribution across all shards. The --sharding-method parameter can also be overriden by setting the key controller.sharding.algorithm in the argocd-cmd-params-cm configMap (preferably) or by setting the ARGOCD_CONTROLLER_SHARDING_ALGORITHM environment variable and by specifiying the same possible values.

Alpha Feature

The round-robin shard distribution algorithm is an experimental feature. Reshuffling is known to occur in certain scenarios with cluster removal. If the cluster at rank-0 is removed, reshuffling all clusters across shards will occur and may temporarily have negative performance impacts.

  • A cluster can be manually assigned and forced to a shard by patching the shard field in the cluster secret to contain the shard number, e.g.
  1. apiVersion: v1
  2. kind: Secret
  3. metadata:
  4.   name: mycluster-secret
  5.   labels:
  6.     argocd.argoproj.io/secret-type: cluster
  7. type: Opaque
  8. stringData:
  9.   shard: 1
  10.   name: mycluster.com
  11.   server: https://mycluster.com
  12.   config: |
  13.     {
  14.       "bearerToken": "<authentication token>",
  15.       "tlsClientConfig": {
  16.         "insecure": false,
  17.         "caData": "<base64 encoded certificate>"
  18.       }
  19.     }
  • ARGOCD_ENABLE_GRPC_TIME_HISTOGRAM - environment variable that enables collecting RPC performance metrics. Enable it if you need to troubleshoot performance issues. Note: This metric is expensive to both query and store!

metrics

  • argocd_app_reconcile - reports application reconciliation duration. Can be used to build reconciliation duration heat map to get a high-level reconciliation performance picture.
  • argocd_app_k8s_request_total - number of k8s requests per application. The number of fallback Kubernetes API queries - useful to identify which application has a resource with non-preferred version and causes performance issues.

argocd-server

The argocd-server is stateless and probably the least likely to cause issues. To ensure there is no downtime during upgrades, consider increasing the number of replicas to 3 or more and repeat the number in the ARGOCD_API_SERVER_REPLICAS environment variable. The strategic merge patch below demonstrates this.

  1. apiVersion: apps/v1
  2. kind: Deployment
  3. metadata:
  4.   name: argocd-server
  5. spec:
  6.   replicas: 3
  7.   template:
  8.     spec:
  9.       containers:
  10.       - name: argocd-server
  11.         env:
  12.         - name: ARGOCD_API_SERVER_REPLICAS
  13.           value: "3"

settings:

  • The ARGOCD_API_SERVER_REPLICAS environment variable is used to divide the limit of concurrent login requests (ARGOCD_MAX_CONCURRENT_LOGIN_REQUESTS_COUNT) between each replica.
  • The ARGOCD_GRPC_MAX_SIZE_MB environment variable allows specifying the max size of the server response message in megabytes. The default value is 200. You might need to increase this for an Argo CD instance that manages 3000+ applications.

argocd-dex-server, argocd-redis

The argocd-dex-server uses an in-memory database, and two or more instances would have inconsistent data. argocd-redis is pre-configured with the understanding of only three total redis servers/sentinels.

Monorepo Scaling Considerations

Argo CD repo server maintains one repository clone locally and uses it for application manifest generation. If the manifest generation requires to change a file in the local repository clone then only one concurrent manifest generation per server instance is allowed. This limitation might significantly slowdown Argo CD if you have a mono repository with multiple applications (50+).

Enable Concurrent Processing

Argo CD determines if manifest generation might change local files in the local repository clone based on the config management tool and application settings. If the manifest generation has no side effects then requests are processed in parallel without a performance penalty. The following are known cases that might cause slowness and their workarounds:

  • Multiple Helm based applications pointing to the same directory in one Git repository: ensure that your Helm chart doesn’t have conditional dependencies and create .argocd-allow-concurrency file in the chart directory.

  • Multiple Custom plugin based applications: avoid creating temporal files during manifest generation and create .argocd-allow-concurrency file in the app directory, or use the sidecar plugin option, which processes each application using a temporary copy of the repository.

  • Multiple Kustomize applications in same repository with parameter overrides: sorry, no workaround for now.

Webhook and Manifest Paths Annotation

Argo CD aggressively caches generated manifests and uses the repository commit SHA as a cache key. A new commit to the Git repository invalidates the cache for all applications configured in the repository. This can negatively affect repositories with multiple applications. You can use webhooks and the argocd.argoproj.io/manifest-generate-paths Application CRD annotation to solve this problem and improve performance.

The argocd.argoproj.io/manifest-generate-paths annotation contains a semicolon-separated list of paths within the Git repository that are used during manifest generation. The webhook compares paths specified in the annotation with the changed files specified in the webhook payload. If no modified files match the paths specified in argocd.argoproj.io/manifest-generate-paths, then the webhook will not trigger application reconciliation and the existing cache will be considered valid for the new commit.

Installations that use a different repository for each application are not subject to this behavior and will likely get no benefit from using these annotations.

Note

Application manifest paths annotation support depends on the git provider used for the Application. It is currently only supported for GitHub, GitLab, and Gogs based repos.

  • Relative path The annotation might contain a relative path. In this case the path is considered relative to the path specified in the application source:
  1. apiVersion: argoproj.io/v1alpha1
  2. kind: Application
  3. metadata:
  4.   name: guestbook
  5.   namespace: argocd
  6.   annotations:
  7.     # resolves to the 'guestbook' directory
  8.     argocd.argoproj.io/manifest-generate-paths: .
  9. spec:
  10.   source:
  11.     repoURL: https://github.com/argoproj/argocd-example-apps.git
  12.     targetRevision: HEAD
  13.     path: guestbook
  14. # ...
  • Absolute path The annotation value might be an absolute path starting with ‘/‘. In this case path is considered as an absolute path within the Git repository:
  1. apiVersion: argoproj.io/v1alpha1
  2. kind: Application
  3. metadata:
  4.   name: guestbook
  5.   annotations:
  6.     argocd.argoproj.io/manifest-generate-paths: /guestbook
  7. spec:
  8.   source:
  9.     repoURL: https://github.com/argoproj/argocd-example-apps.git
  10.     targetRevision: HEAD
  11.     path: guestbook
  12. # ...
  • Multiple paths It is possible to put multiple paths into the annotation. Paths must be separated with a semicolon (;):
  1. apiVersion: argoproj.io/v1alpha1
  2. kind: Application
  3. metadata:
  4.   name: guestbook
  5.   annotations:
  6.     # resolves to 'my-application' and 'shared'
  7.     argocd.argoproj.io/manifest-generate-paths: .;../shared
  8. spec:
  9.   source:
  10.     repoURL: https://github.com/argoproj/argocd-example-apps.git
  11.     targetRevision: HEAD
  12.     path: my-application
  13. # ...