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https://issues.apache.org/jira/browse/CURATOR-394?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15938967#comment-15938967
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Gian Merlino commented on CURATOR-394:
--------------------------------------
I think doing a 2.12.1 that reverts CURATOR-275 would fix the compatibility
problem and let old clients talk to new services again.
As for how to get something like CURATOR-275 back in, I think a long term fix
has to involve disabling Jackson's {{FAIL_ON_UNKNOWN_PROPERTIES}}
(https://github.com/FasterXML/jackson-databind/wiki/Deserialization-Features),
or doing something with similar effect, when Curator deserializes objects that
might have new fields added in future versions. Otherwise, fields added in
newer versions will keep breaking older clients.
I think there's a couple options,
1. In some Curator version X, disable FAIL_ON_UNKNOWN_PROPERTIES for
ServiceInstance deserialization. Then, in some Curator version Y > X, a field
could be added. Users will need to be told that to upgrade services to version
Y, all clients must be at least on version X. So an upgrade from a version < X
could be done by users in two waves, first upgrading to X and then to Y. After
that point, the old code isn't running anymore and the problem is gone.
2. Curator could avoid telling users to do that dance above by continuing to
support announcing ServiceInstances in their existing form, in their existing
location, basically forever, but deprecating that form and location. Then
create a new ServiceInstance2 that, from the start, has
FAIL_ON_UNKNOWN_PROPERTIES enabled. Add all new fields to that class and don't
update ServiceInstance. With this approach, users don't have to upgrade clients
through some specific version X first, but services do have to announce
themselves using two different formats.
I'm not sure if there's a simpler way to get new fields added in a manner that
avoids having to always upgrade clients first.
> UnrecognizedPropertyException: "enabled" incompatibility
> --------------------------------------------------------
>
> Key: CURATOR-394
> URL: https://issues.apache.org/jira/browse/CURATOR-394
> Project: Apache Curator
> Issue Type: Bug
> Components: Recipes
> Affects Versions: 2.12.0
> Reporter: Gian Merlino
>
> When doing a rolling upgrade of our services from Curator 2.10.0 to Curator
> 2.12.0 we noticed some of the non-upgraded services started throwing this
> error. The cause seems to the combination of a new field added to
> ServiceInstance in CURATOR-275, and the lack of an "ignore unknown
> properties" setting on the ObjectMapper used by Curator 2.10.0.
> This makes it so clients need to be upgraded before services. But if you have
> a cluster where some services are also clients of other services (or of a
> service they are a part of) then I don't see a way to do a rolling upgrade
> with the way things currently are. Whatever instance you upgrade first will
> start announcing itself in a way that breaks instances running the previous
> version of the code. This doesn't seem to be configurable either, so the new
> "enabled" field can't be omitted from the serialized form.
> One possible solution is to revert CURATOR-275, add an "ignore unknown
> properties" to the ObjectMapper, and then re-introduce CURATOR-275 in a
> future release. That'd create a "you must go through release X first to
> upgrade to release Y" situation, but it would at least make it possible to do
> rolling updates.
> Another possible solution is to accept that clients always need to be
> upgraded before services, and accept that if you can't do this, it's
> impossible to update without downtime. This seems like something that'd be
> good to avoid though.
> {code}
> 2017-03-23 16:22:35,652
> [DruidTaskResolver[com.metamx.tranquility.druid.IndexService@37a0ec3c]] WARN
> c.m.t.finagle.DruidTaskResolver - Poll failed, trying again
> at[2017-03-23T16:23:10.899Z].
> org.codehaus.jackson.map.exc.UnrecognizedPropertyException: Unrecognized
> field "enabled" (Class org.apache.curator.x.discovery.ServiceInstance), not
> marked as ignorable
> at [Source: [B@e9cde06; line: 1, column: 226] (through reference chain:
> org.apache.curator.x.discovery.ServiceInstance["enabled"])
> at
> org.codehaus.jackson.map.exc.UnrecognizedPropertyException.from(UnrecognizedPropertyException.java:53)
> ~[org.codehaus.jackson.jackson-mapper-asl-1.9.13.jar:1.9.13]
> at
> org.codehaus.jackson.map.deser.StdDeserializationContext.unknownFieldException(StdDeserializationContext.java:267)
> ~[org.codehaus.jackson.jackson-mapper-asl-1.9.13.jar:1.9.13]
> at
> org.codehaus.jackson.map.deser.std.StdDeserializer.reportUnknownProperty(StdDeserializer.java:673)
> ~[org.codehaus.jackson.jackson-mapper-asl-1.9.13.jar:1.9.13]
> at
> org.codehaus.jackson.map.deser.std.StdDeserializer.handleUnknownProperty(StdDeserializer.java:659)
> ~[org.codehaus.jackson.jackson-mapper-asl-1.9.13.jar:1.9.13]
> at
> org.codehaus.jackson.map.deser.BeanDeserializer.handleUnknownProperty(BeanDeserializer.java:1365)
> ~[org.codehaus.jackson.jackson-mapper-asl-1.9.13.jar:1.9.13]
> at
> org.codehaus.jackson.map.deser.BeanDeserializer._handleUnknown(BeanDeserializer.java:725)
> ~[org.codehaus.jackson.jackson-mapper-asl-1.9.13.jar:1.9.13]
> at
> org.codehaus.jackson.map.deser.BeanDeserializer.deserializeFromObject(BeanDeserializer.java:703)
> ~[org.codehaus.jackson.jackson-mapper-asl-1.9.13.jar:1.9.13]
> at
> org.codehaus.jackson.map.deser.BeanDeserializer.deserialize(BeanDeserializer.java:580)
> ~[org.codehaus.jackson.jackson-mapper-asl-1.9.13.jar:1.9.13]
> at
> org.codehaus.jackson.map.ObjectMapper._readMapAndClose(ObjectMapper.java:2732)
> ~[org.codehaus.jackson.jackson-mapper-asl-1.9.13.jar:1.9.13]
> at
> org.codehaus.jackson.map.ObjectMapper.readValue(ObjectMapper.java:1973)
> ~[org.codehaus.jackson.jackson-mapper-asl-1.9.13.jar:1.9.13]
> at
> org.apache.curator.x.discovery.details.JsonInstanceSerializer.deserialize(JsonInstanceSerializer.java:50)
> ~[org.apache.curator.curator-x-discovery-2.10.0.jar:na]
> at
> org.apache.curator.x.discovery.details.ServiceCacheImpl.addInstance(ServiceCacheImpl.java:193)
> ~[org.apache.curator.curator-x-discovery-2.10.0.jar:na]
> at
> org.apache.curator.x.discovery.details.ServiceCacheImpl.start(ServiceCacheImpl.java:96)
> ~[org.apache.curator.curator-x-discovery-2.10.0.jar:na]
> {code}
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