0ac8ae6c3b
* Fix xDS deadlock due to syncLoop termination. This fixes an issue where agentless xDS streams can deadlock permanently until a server is restarted. When this issue occurs, no new proxies are able to successfully connect to the server. Effectively, the trigger for this deadlock stems from the following return statement: https://github.com/hashicorp/consul/blob/v1.18.0/agent/proxycfg-sources/catalog/config_source.go#L199-L202 When this happens, the entire `syncLoop()` terminates and stops consuming from the following channel: https://github.com/hashicorp/consul/blob/v1.18.0/agent/proxycfg-sources/catalog/config_source.go#L182-L192 Which results in the `ConfigSource.cleanup()` function never receiving a response and holding a mutex indefinitely: https://github.com/hashicorp/consul/blob/v1.18.0/agent/proxycfg-sources/catalog/config_source.go#L241-L247 Because this mutex is shared, it effectively deadlocks the server's ability to process new xDS streams. ---- The fix to this issue involves removing the `chan chan struct{}` used like an RPC-over-channels pattern and replacing it with two distinct channels: + `stopSyncLoopCh` - indicates that the `syncLoop()` should terminate soon. + `syncLoopDoneCh` - indicates that the `syncLoop()` has terminated. Splitting these two concepts out and deferring a `close(syncLoopDoneCh)` in the `syncLoop()` function ensures that the deadlock above should no longer occur. We also now evict xDS connections of all proxies for the corresponding `syncLoop()` whenever it encounters an irrecoverable error. This is done by hoisting the new `syncLoopDoneCh` upwards so that it's visible to the xDS delta processing. Prior to this fix, the behavior was to simply orphan them so they would never receive catalog-registration or service-defaults updates. * Add changelog. |
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README.md
Consul
Consul is a distributed, highly available, and data center aware solution to connect and configure applications across dynamic, distributed infrastructure.
- Website: https://www.consul.io
- Tutorials: HashiCorp Learn
- Forum: Discuss
Consul provides several key features:
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Multi-Datacenter - Consul is built to be datacenter aware, and can support any number of regions without complex configuration.
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Service Mesh - Consul Service Mesh enables secure service-to-service communication with automatic TLS encryption and identity-based authorization. Applications can use sidecar proxies in a service mesh configuration to establish TLS connections for inbound and outbound connections with Transparent Proxy.
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API Gateway - Consul API Gateway manages access to services within Consul Service Mesh, allow users to define traffic and authorization policies to services deployed within the mesh.
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Service Discovery - Consul makes it simple for services to register themselves and to discover other services via a DNS or HTTP interface. External services such as SaaS providers can be registered as well.
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Health Checking - Health Checking enables Consul to quickly alert operators about any issues in a cluster. The integration with service discovery prevents routing traffic to unhealthy hosts and enables service level circuit breakers.
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Dynamic App Configuration - An HTTP API that allows users to store indexed objects within Consul, for storing configuration parameters and application metadata.
Consul runs on Linux, macOS, FreeBSD, Solaris, and Windows and includes an optional browser based UI. A commercial version called Consul Enterprise is also available.
Please note: We take Consul's security and our users' trust very seriously. If you believe you have found a security issue in Consul, please responsibly disclose by contacting us at security@hashicorp.com.
Quick Start
A few quick start guides are available on the Consul website:
- Standalone binary install: https://learn.hashicorp.com/collections/consul/get-started-vms
- Minikube install: https://learn.hashicorp.com/tutorials/consul/kubernetes-minikube
- Kind install: https://learn.hashicorp.com/tutorials/consul/kubernetes-kind
- Kubernetes install: https://learn.hashicorp.com/tutorials/consul/kubernetes-deployment-guide
- Deploy HCP Consul: https://learn.hashicorp.com/tutorials/consul/hcp-gs-deploy
Documentation
Full, comprehensive documentation is available on the Consul website: https://consul.io/docs
Contributing
Thank you for your interest in contributing! Please refer to CONTRIBUTING.md for guidance. For contributions specifically to the browser based UI, please refer to the UI's README.md for guidance.