mirror of https://github.com/k3s-io/k3s
85 lines
4.2 KiB
Markdown
85 lines
4.2 KiB
Markdown
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# flannel
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[](https://travis-ci.org/coreos/flannel)
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Flannel is a simple and easy way to configure a layer 3 network fabric designed for Kubernetes.
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## How it works
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Flannel runs a small, single binary agent called `flanneld` on each host, and is responsible for allocating a subnet lease to each host out of a larger, preconfigured address space.
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Flannel uses either the Kubernetes API or [etcd][etcd] directly to store the network configuration, the allocated subnets, and any auxiliary data (such as the host's public IP).
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Packets are forwarded using one of several [backend mechanisms][backends] including VXLAN and various cloud integrations.
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### Networking details
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Platforms like Kubernetes assume that each container (pod) has a unique, routable IP inside the cluster.
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The advantage of this model is that it removes the port mapping complexities that come from sharing a single host IP.
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Flannel is responsible for providing a layer 3 IPv4 network between multiple nodes in a cluster. Flannel does not control how containers are networked to the host, only how the traffic is transported between hosts. However, flannel does provide a CNI plugin for Kubernetes and a guidance on integrating with Docker.
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Flannel is focused on networking. For network policy, other projects such as [Calico][calico] can be used.
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## Getting started on Kubernetes
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The easiest way to deploy flannel with Kubernetes is to use one of several deployment tools and distributions that network clusters with flannel by default. For example, CoreOS's [Tectonic][tectonic] sets up flannel in the Kubernetes clusters it creates using the open source [Tectonic Installer][tectonic-installer] to drive the setup process.
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Though not required, it's recommended that flannel uses the Kubernetes API as its backing store which avoids the need to deploy a discrete `etcd` cluster for `flannel`. This `flannel` mode is known as the *kube subnet manager*.
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### Deploying flannel manually
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Flannel can be added to any existing Kubernetes cluster though it's simplest to add `flannel` before any pods using the pod network have been started.
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For Kubernetes v1.7+
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`kubectl apply -f https://raw.githubusercontent.com/coreos/flannel/master/Documentation/kube-flannel.yml`
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See [Kubernetes](Documentation/kubernetes.md) for more details.
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## Getting started on Docker
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flannel is also widely used outside of kubernetes. When deployed outside of kubernetes, etcd is always used as the datastore. For more details integrating flannel with Docker see [Running](Documentation/running.md)
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## Documentation
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- [Building (and releasing)](Documentation/building.md)
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- [Configuration](Documentation/configuration.md)
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- [Backends](Documentation/backends.md)
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- [Running](Documentation/running.md)
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- [Troubleshooting](Documentation/troubleshooting.md)
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- [Projects integrating with flannel](Documentation/integrations.md)
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- [Production users](Documentation/production-users.md)
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## Contact
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* Mailing list: coreos-dev
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* IRC: #coreos on freenode.org
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* Slack: #flannel on [Calico Users Slack](https://slack.projectcalico.org)
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* Planning/Roadmap: [milestones][milestones], [roadmap][roadmap]
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* Bugs: [issues][flannel-issues]
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## Contributing
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See [CONTRIBUTING][contributing] for details on submitting patches and the contribution workflow.
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## Reporting bugs
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See [reporting bugs][reporting] for details about reporting any issues.
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## Licensing
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Flannel is under the Apache 2.0 license. See the [LICENSE][license] file for details.
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[calico]: http://www.projectcalico.org
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[pod-cidr]: https://kubernetes.io/docs/admin/kubelet/
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[etcd]: https://github.com/coreos/etcd
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[contributing]: CONTRIBUTING.md
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[license]: https://github.com/coreos/flannel/blob/master/LICENSE
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[milestones]: https://github.com/coreos/flannel/milestones
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[flannel-issues]: https://github.com/coreos/flannel/issues
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[backends]: Documentation/backends.md
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[roadmap]: https://github.com/kubernetes/kubernetes/milestones
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[reporting]: Documentation/reporting_bugs.md
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[tectonic-installer]: https://github.com/coreos/tectonic-installer
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[installing-with-kubeadm]: https://kubernetes.io/docs/getting-started-guides/kubeadm/
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[tectonic]: https://coreos.com/tectonic/
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