mirror of https://github.com/k3s-io/k3s
44 lines
2.2 KiB
Markdown
44 lines
2.2 KiB
Markdown
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# Package spegel Distributed Registry Mirror
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Date: 2023-12-07
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## Status
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Accepted
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## Context
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Embedded registry mirror support has been on the roadmap for some time, to address multiple challenges:
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* Upstream registries may enforce pull limits or otherwise throttle access to images.
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* In edge scenarios, bandwidth is at a premium, if external access is available at all.
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* Distributing airgap image tarballs to nodes, and ensuring that images remain available, is an ongoing
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hurdle to adoption.
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* Deploying an in-cluster registry, or hosting a registry outside the cluster, put significant
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burden on administrators, and suffer from chicken-or-egg bootstrapping issues.
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An ideal embedded registry would have several characteristics:
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* Allow stateless configuration such that nodes can come and go at any time.
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* Integrate into existing containerd registry mirror support.
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* Integrate into existing containerd image stores such that an additional copy of layer data is not required.
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* Use existing cluster authentication mechanisms to prevent unauthorized access to the registry.
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* Operate with minimal added CPU and memory overhead.
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## Decision
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* We will embed spegel within K3s, and use it to host a distributed registry mirror.
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* The distributed registry mirror will be enabled cluster-wide via server CLI flag.
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* Selection of upstream registries to mirror will be implemented via the existing `registries.yaml`
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configuration file.
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* The registry API will be served via HTTPS on every node's private IP at port 6443. On servers this will
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use the existing supervisor listener; on agents a new listener will be created for this purpose.
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* The default IPFS/libp2p port of 5001 will be used for P2P layer discovery.
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* Access to the registry API and P2P network will require proof of cluster membership, enforced via
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client certificate or preshared key.
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* Hybrid/multicloud support is out of scope; when the distributed registry mirror is enabled, cluster
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members are assumed to be directly accessible to each other via their internal IP on the listed ports.
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## Consequences
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* The size of our self-extracting binary and Docker images increase by several megabytes.
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* We take on the support burden of keeping spegel up to date, and supporting its use within K3s.
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