44 lines
2.3 KiB
Plaintext
44 lines
2.3 KiB
Plaintext
---
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layout: docs
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page_title: Consul Protocol Compatibility Promise
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description: >-
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We expect Consul to run in large clusters of long-running agents. Because
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safely upgrading agents in this sort of environment relies heavily on
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backwards compatibility, we have a strong commitment to keeping different
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Consul versions protocol-compatible with each other.
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---
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# Protocol Compatibility Promise
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We expect Consul to run in large clusters of long-running agents. Because
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safely upgrading agents in this sort of environment relies heavily on backwards
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compatibility, we have a strong commitment to keeping different Consul
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versions protocol-compatible with each other.
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We promise that every subsequent release of Consul will remain backwards
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compatible with _at least_ one prior version. Concretely: version 0.5 can
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speak to 0.4 (and vice versa) but may not be able to speak to 0.1.
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Backwards compatibility is automatic unless otherwise noted. Consul agents by
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default will speak the latest protocol but can understand earlier ones.
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-> **Note:** If speaking an earlier protocol, _new features may not be available_.
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The ability for an agent to speak an earlier protocol is to ensure that any agent
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can be upgraded without cluster disruption. Consul agents can be updated one
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at a time, one version at a time.
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For more details on the specifics of upgrading, see the [upgrading page](/docs/upgrading).
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## Protocol Compatibility Table
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| Consul Version | Protocol Compatibility |
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| -------------- | ---------------------------------------------------------------------------- |
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| 0.1 - 0.3 | 1 |
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| 0.4 | 1, 2 |
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| 0.5 | 1, 2. 0.5.X servers cannot be mixed with older servers. |
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| 0.6 | 1, 2, 3 |
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| >= 0.7 | 2, 3. Will automatically use protocol > 2 when speaking to compatible agents |
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-> **Note:** Raft Protocol is versioned separately, but maintains compatibility with at least one prior version. See [here](/docs/upgrading/upgrade-specific#raft-protocol-version-compatibility) for details.
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