[SERVER-37658] Mongos 3.6 requires min and max wire version to be 6 (6,6) Created: 18/Oct/18 Updated: 27/Oct/23 Resolved: 18/Oct/18 |
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| Status: | Closed |
| Project: | Core Server |
| Component/s: | Internal Code |
| Affects Version/s: | 3.6.7 |
| Fix Version/s: | None |
| Type: | Bug | Priority: | Major - P3 |
| Reporter: | Rob Manning | Assignee: | Kaloian Manassiev |
| Resolution: | Works as Designed | Votes: | 0 |
| Labels: | None | ||
| Remaining Estimate: | Not Specified | ||
| Time Spent: | Not Specified | ||
| Original Estimate: | Not Specified | ||
| Operating System: | ALL |
| Steps To Reproduce: |
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| Participants: |
| Description |
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When performing a rolling downgrade on a version 3.6.7 cluster to version 3.4, once the config servers and shards have all been downgraded, the remaining version 3.6 mongos nodes can no longer connect to the cluster. This can be seen in the mongos.log: <timestamp> W NETWORK [UserCacheInvalidator] remote host has incompatible wire version: IncompatibleServerVersion: Server min and max wire version are incompatible (0,5) with client min wire version (6,6). However, when connecting to a version 3.6.7 mongod and running the command db.isMaster(), the resulting document shows "minWireVersion" : 0, "maxWireVersion" : 6. This makes it impossible to perform a rolling downgrade from 3.6.7 to 3.4.x without taking an outage, as all mongos nodes become unusable from the time that the config servers are downgraded until the time that at least one mongos is downgraded. |
| Comments |
| Comment by Kaloian Manassiev [ 18/Oct/18 ] |
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Yes, for all versions from 3.2 onwards the order of downgrade is first mongos, then shards, then config server (inverse to the order for upgrade). |
| Comment by Rob Manning [ 18/Oct/18 ] |
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Ahhhh! So the upgrade and downgrade procedures differ with regard to the order of different types of nodes (particularly mongos). That's unfortunate for our internal update automation. Is this also the case for downgrades from 4.0 to 3.6? |
| Comment by Kaloian Manassiev [ 18/Oct/18 ] |
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Hi wideningartist9, What you are experiencing is expected, because 3.6 mongos is not allowed to talk to 3.4 shards/config server. The downgrade instructions here state that the first thing, which needs to be downgraded after FCV is set to 3.4 are the mongos instances. Hope this helps. -Kal. |