f52912454d
The CSI specification says that we "SHOULD" send no more than one in-flight request per *volume* at a time, with an allowance for losing state (ex. leadership transitions) which the plugins "SHOULD" handle gracefully. We mostly successfully serialize node and controller RPCs for the same volume, except when Nomad clients are lost. (See also https://github.com/container-storage-interface/spec/issues/512) These concurrency requirements in the spec fall short because Storage Provider APIs aren't necessarily safe to call concurrently on the same host even for _different_ volumes. For example, concurrently attaching AWS EBS volumes to an EC2 instance results in a race for device names, which results in failure to attach (because the device name is taken already and the API call fails) and confused results when releasing claims. So in practice many CSI plugins rely on k8s-specific sidecars for serializing storage provider API calls globally. As a result, we have to be much more conservative about concurrency in Nomad than the spec allows. This changeset includes four major changes to fix this: * Add a serializer method to the CSI volume RPC handler. When the RPC handler makes a destructive CSI Controller RPC, we send the RPC thru this serializer and only one RPC is sent at a time. Any other RPCs in flight will block. * Ensure that requests go to the same controller plugin instance whenever possible by sorting by lowest client ID out of the plugin instances. * Ensure that requests go to _healthy_ plugin instances only. * Ensure that requests for controllers can go to a controller on any _live_ node, not just ones eligible for scheduling (which CSI controllers don't care about) Fixes: #15415
Nomad
Nomad is a simple and flexible workload orchestrator to deploy and manage containers (docker, podman), non-containerized applications (executable, Java), and virtual machines (qemu) across on-prem and clouds at scale.
Nomad is supported on Linux, Windows, and macOS. A commercial version of Nomad, Nomad Enterprise, is also available.
- Website: https://nomadproject.io
- Tutorials: HashiCorp Learn
- Forum: Discuss
Nomad provides several key features:
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Deploy Containers and Legacy Applications: Nomad’s flexibility as an orchestrator enables an organization to run containers, legacy, and batch applications together on the same infrastructure. Nomad brings core orchestration benefits to legacy applications without needing to containerize via pluggable task drivers.
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Simple & Reliable: Nomad runs as a single binary and is entirely self contained - combining resource management and scheduling into a single system. Nomad does not require any external services for storage or coordination. Nomad automatically handles application, node, and driver failures. Nomad is distributed and resilient, using leader election and state replication to provide high availability in the event of failures.
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Device Plugins & GPU Support: Nomad offers built-in support for GPU workloads such as machine learning (ML) and artificial intelligence (AI). Nomad uses device plugins to automatically detect and utilize resources from hardware devices such as GPU, FPGAs, and TPUs.
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Federation for Multi-Region, Multi-Cloud: Nomad was designed to support infrastructure at a global scale. Nomad supports federation out-of-the-box and can deploy applications across multiple regions and clouds.
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Proven Scalability: Nomad is optimistically concurrent, which increases throughput and reduces latency for workloads. Nomad has been proven to scale to clusters of 10K+ nodes in real-world production environments.
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HashiCorp Ecosystem: Nomad integrates seamlessly with Terraform, Consul, Vault for provisioning, service discovery, and secrets management.
Quick Start
Testing
See Learn: Getting Started for instructions on setting up a local Nomad cluster for non-production use.
Optionally, find Terraform manifests for bringing up a development Nomad cluster on a public cloud in the terraform directory.
Production
See Learn: Nomad Reference Architecture for recommended practices and a reference architecture for production deployments.
Documentation
Full, comprehensive documentation is available on the Nomad website: https://www.nomadproject.io/docs
Guides are available on HashiCorp Learn.
Roadmap
A timeline of major features expected for the next release or two can be found in the Public Roadmap.
This roadmap is a best guess at any given point, and both release dates and projects in each release are subject to change. Do not take any of these items as commitments, especially ones later than one major release away.
Contributing
See the contributing directory for more developer documentation.