Architecture
Keptn is an event-based control plane for continuous delivery and automated operations that runs on Kubernetes. When installing Keptn on a Kubernetes cluster, core components, and Istio are installed. Keptn itself follows an event-driven approach with the benefits of loosely coupled components and a flexible design that allows easily integrating other components and services. The events that Keptn understands are specified here and follow the CloudEvents specification v2.
Prerequisites
During a Keptn installation, the following components are installed on the Kubernetes cluster:
Keptn CLI
The Keptn CLI needs to be installed on the local machine and is used to send commands to Keptn by interacting with the API of Keptn. To communicate with Keptn you need to know a shared secret that is generated during the installation and verified by the api component.
Note: A dedicated Keptn CLI section is provided here, which helps you to get started and lists all available commands.
Keptn core components
Keptn has several core components that are set up during the installation.
api
The api component provides a publicly exposed REST API that allows communicating with Keptn. It receives the commands from the CLI and executes the requested tasks. However, the api component mostly uses other internal services or forwards events to the eventbroker. In addition to the REST API, the api component maintains a websocket server to forward Keptn messages to the Keptn CLI.
Note: A dedicated Keptn API section is provided here, which helps you to access the API and to explore the available endpoints.
eventbroker
The eventbroker is responsible for receiving all events and sending those into NATS.
distributor
A distributor receives events from NATS and sends the events to services that have a subscription to the event topic. Consequently, each service has its distributor that is configured for the events to receive.
mongodb-datastore
The mongodb-datastore provides means to store event data in a MongoDB deployed in your Keptn cluster. Hence, the service provides the REST endpoint /events to query events.
bridge
The Keptn Bridge provides a user interface that shows all Keptn-managed projects and services. Besides, it gives an overview of the staging environment.
Note: A dedicated section for the Keptn Bridge is provided here, which explains how to access it and shows the user interface.
configuration-service
The configuration-service is a Keptn core component and used to manage resources for Keptn project-related entities, i.e., project, stage, and service. The entity model is shown below. To store the resources with version control, a Git repository is used that is mounted as a persistent volume. Besides, this service has the functionality to upload the Git repository to any Git-based service such as GitLab, GitHub, Bitbucket, etc.
Entity model
------------ ------------ ------------
| | 1 | | 1 | |
| Project |----------| Stage |----------| Service |
| | * | | * | |
------------ ------------ ------------
1 \ 1 \ 1 \
\ * \ * \ *
------------ ------------ ------------
| | | | | |
| Resource | | Resource | | Resource |
| | | | | |
------------ ------------ ------------
internal-keptn-services
This category of services reacts on Keptn events and perform: (1) initial tasks like creating a project or creating a service, (2) continuous delivery tasks like deploying or promoting a service, and (3) orchestrational tasks for automating operations.
shipyard-service: It is responsible for creating a project and processing a shipyard file that defines the stages each deployment has to go through until it is released to end-users.
helm-service: It has two responsibilities: (1) creates/modifies the configuration of a service that is going to be onboarded, and (2) fetches configuration files from the configuration-service and applies those using Helm. The current Helm version used by this service is Helm v3.1.2.
wait-service: It is responsible for delaying a Keptn workflow for a specified duration.
gatekeeper-service: It implements the quality gate in each stage, i.e., depending on the evaluation result it either promotes an artifact to the next stage or not.
remediation-service: It is used to orchestrate remediation workflows.
Keptn services
To enrich the continuous delivery use case or to build automated operations, Keptn relies on services from the community. Those services can be easily plugged into the workflows to extend the delivery pipeline or to further automate operations.
Note: A dedicated tutorial is provided here, which helps you to implement a custom service for Keptn.
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