61 lines
2.2 KiB
Markdown
61 lines
2.2 KiB
Markdown
---
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layout: "docs"
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page_title: "Consul Protocol Compatibility Promise"
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sidebar_current: "docs-upgrading-compatibility"
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description: |-
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We expect Consul to run in large clusters of long-running agents. Because safely upgrading agents in this sort of environment relies heavily on backwards compatibility, we have a strong commitment to keeping different 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.html).
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## Protocol Compatibility Table
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<table class="table table-bordered table-striped">
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<tr>
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<th>Version</th>
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<th>Protocol Compatibility</th>
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</tr>
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<tr>
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<td>0.1 - 0.3</td>
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<td>1</td>
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</tr>
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<td>0.4</td>
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<td>1, 2</td>
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</tr>
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<tr>
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<td>0.5</td>
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<td>1, 2. 0.5.X servers cannot be mixed with older servers.</td>
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</tr>
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<tr>
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<td>0.6</td>
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<td>1, 2, 3</td>
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</tr>
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<tr>
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<td>0.7 - 0.8</td>
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<td>2, 3. Will automatically use protocol > 2 when speaking to compatible agents</td>
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</tr>
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</table>
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-> **Note:** Raft Protocol is versioned separately, but maintains compatibility with at least one prior version. See [here](https://www.consul.io/docs/upgrade-specific.html#raft-protocol-version-compatibility) for details.
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