Diego Components and Architecture
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This topic provides an overview of the structure and components of Diego, the new container management system for Cloud Foundry.
This topic includes the following sections:
- Architecture Diagram
- Diego Components
- Platform-specific Components
Cloud Foundry uses the Diego architecture to manage application containers. Diego components assume application scheduling and management responsibility from the Cloud Controller.
Refer to the following diagram and descriptions for information about the way Diego handles application requests.
The Cloud Controller passes requests to stage and run applications to several components on the Diego Brain.
The BBS tracks desired LRPs, running LRP instances, and in-flight Tasks. It also periodically analyzes this information and corrects discrepancies to ensure consistency between
Diego components run and monitor Tasks and LRPs.
Diego Brain components distribute Tasks and LRPs to Diego Cells, and correct discrepancies between
DesiredLRP counts to ensure fault-tolerance and long-term consistency.
The Diego Brain consists of the following:
Uses the auction package to run Diego Auctions for Tasks and LRPs
Communicates with Cell Reps over SSL/TLS
Maintains a lock in the BBS that restricts auctions to one Auctioneer at a time
Refer to the Auctioneer repository on GitHub for more information.
Mediates uploads from the Executor to the Cloud Controller
Translates simple HTTP POST requests from the Executor into complex multipart-form uploads for the Cloud Controller
Refer to the CC-Uploader repository on GitHub for more information.
- This “blobstore” serves static assets that can include general-purpose App Lifecycle binaries and application-specific droplets and build artifacts.
Refer to the File Server repository on GitHub for more information.
- Brokers connections between SSH clients and SSH servers running inside instance containers
Provides the Cloud Controller with information about currently running LRPs to respond to
cf app APP_NAMErequests
ActualLRPactivity for crashes and reports them the Cloud Controller
Refer to the TPS repository on GitHub for more information.
ActualLRPstates, emitting TCP route registration and unregistration messages to the Cloud Foundry routing API when it detects changes
Periodically emits TCP routes to the Cloud Foundry routing API
Listens for app requests to update the
DesiredLRPscount and updates
DesiredLRPsthrough the BBS
Periodically polls the Cloud Controller for each app to ensure that Diego maintains accurate
Refer to the Nsync repository on GitHub for more information.
Translates staging requests from the Cloud Controller into generic Tasks and LRPs
Sends a response to the Cloud Controller when a Task completes
Refer to the Stager repository on GitHub for more information.
Diego Cell components manage and maintain Tasks and LRPs.
The Diego Cell consists of the following:
Represents a Cell in Diego Auctions for Tasks and LRPs
Mediates all communication between the Cell and the BBS
Ensures synchronization between the set of Tasks and LRPs in the BBS with the containers present on the Cell
Maintains the presence of the Cell in the BBS
Runs Tasks and LRPs by asking the in-process Executor to create a container and
Refer to the Rep repository on GitHub for more information.
Runs as a logical process inside the Rep
Implements the generic Executor actions detailed in the API documentation
STDERRto the Metron agent running on the Cell
Refer to the Executor repository on GitHub for more information.
Provides a platform-independent server and clients to manage Garden containers
Defines the Garden-runC interface for container implementation
Forwards application logs, errors, and application and Diego metrics to the Loggregator Doppler component
Refer to the Metron repository on GitHub for more information.
ActualLRPstates, emitting route registration and unregistration messages to the Cloud Foundry Gorouter when it detects changes
Periodically emits the entire routing table to the Cloud Foundry Gorouter
Refer to the Route-Emitter repository on GitHub for more information.
The Diego database VM consists of the following components.
Maintains a real-time representation of the state of the Diego cluster, including all desired LRPs, running LRP instances, and in-flight Tasks
Ensure consistency and fault tolerance for Tasks and LRPs by comparing desired state (stored in the database) with actual state (from running instances)
Acts to keep
ActualLRPcount synchronized in the following ways:
- If the
DesiredLRPcount exceeds the
ActualLRPcount, requests a start auction from the Auctioneer
- If the
ActualLRPcount exceeds the
DesiredLRPcount, sends a stop message to the Rep on the Cell hosting an instance
- If the
Monitors for potentially missed messages, resending them if necessary
Refer to the Bulletin Board System repository on GitHub for more information.
- Provides a consistent key-value data store to Diego
- Provides a consistent key-value store for maintenance of distributed locks and component presence
The Diego BBS stores data in MySQL. Diego uses the Go MySQL Driver to communicate with MySQL.
Refer to the Go MySQL Driver repository on GitHub for more information.
- Provides dynamic service registration and load balancing through DNS resolution
Refer to the Consul repository on GitHub for more information.
The following three platform-specific binaries deploy applications and govern their lifecycle:
The Builder, which stages a CF application. The Builder runs as a Task on every staging request. It performs static analysis on the application code and does any necessary pre-processing before the application is first run.
The Launcher, which runs a CF application. The Launcher is set as the Action on the
DesiredLRPfor the application. It executes the start command with the correct system context, including working directory and environment variables.
The Healthcheck, which performs a status check on running CF application from inside the container. The Healthcheck is set as the Monitor action on the
DesiredLRPfor the application.