C0urante commented on code in PR #14068:
URL: https://github.com/apache/kafka/pull/14068#discussion_r1286204067
##########
docs/connect.html:
##########
@@ -543,6 +543,67 @@ <h6>ACL requirements</h6>
</tbody>
</table>
+ <h4><a id="connect_plugindiscovery" href="#connect_plugindiscovery">Plugin
Discovery</a></h4>
+
+ <p>Plugin discovery is the name for the strategy which the Connect worker
uses to find plugin classes and make them accessible to configure and run in
connectors. This is controlled by the <a
href="#connectconfigs_plugin.discovery">plugin.discovery</a> worker
configuration, and has a significant impact on worker startup time.
<code>service_load</code> is the fastest strategy, but will hide incompatible
plugins and may make some unusable. Care should be taken to verify that plugins
are compatible before setting this configuration to
<code>service_load</code>.</p>
+
+ <p>Prior to version 3.6, this strategy was not configurable, and behaved
like the <code>only_scan</code> mode which is compatible with all plugins. For
version 3.6 and later, this mode defaults to <code>hybrid_warn</code> which is
also compatible with all plugins, but logs a warning for plugins which are
incompatible with <code>service_load</code>. The <code>hybrid_fail</code>
strategy stops the worker with an error if a plugin incompatible with
<code>service_load</code> is detected, asserting that all plugins are
compatible. Finally, the <code>service_load</code> strategy will hide
incompatible plugins in the REST API, and may make some unusable entirely.</p>
Review Comment:
I don't love the level of detail in "hide incompatible plugins in the REST
API, and may make some unusable entirely", since this isn't really behavior
that we've implemented intentionally. I'd rather be more general here and just
say "may make some plugins unusable"; IMO the term "unusable" gives us enough
wiggle room that it covers both "completely" unusable (i.e., unloadable) and
"partially" unusable (i.e., hidden but loadable).
##########
docs/connect.html:
##########
@@ -543,6 +543,67 @@ <h6>ACL requirements</h6>
</tbody>
</table>
+ <h4><a id="connect_plugindiscovery" href="#connect_plugindiscovery">Plugin
Discovery</a></h4>
+
+ <p>Plugin discovery is the name for the strategy which the Connect worker
uses to find plugin classes and make them accessible to configure and run in
Connectors and Tasks. This is controlled by the <a
href="#connectconfigs_plugin.discovery"><code>plugin.discovery</code> worker
configuration</a>, and has a significant impact on worker startup time.
<code>SERVICE_LOAD</code> is the fastest strategy, but care should be taken to
verify that plugins are compatible before setting this configuration to
<code>SERVICE_LOAD</code>.</p>
+
+ <p>Prior to version 3.6, this strategy was not configurable, and behaved
like the <code>ONLY_SCAN</code> mode which is compatible with all plugins. For
version 3.6 and later, this mode defaults to <code>HYBRID_WARN</code> which is
also compatible with all plugins, but logs a warning for all plugins which are
incompatible with the other modes. For unit-test environments that use the
<code>EmbeddedConnectCluster</code> this defaults to the
<code>HYBRID_FAIL</code> strategy, which stops the worker with an error if an
incompatible plugin is detected. Finally, the <code>SERVICE_LOAD</code>
strategy will silently hide incompatible plugins and make them unusable.</p>
Review Comment:
> I think that including "incompatible with service_load" is less correct
but less confusing.
My take is that in general, it's okay to provide information that is not
comprehensive but, within a limited scope, accurate. The idea is to only cover
scenarios that are highly relevant to users. For example: yes, it's technically
correct that plugins without manifests are incompatible with `hybrid_warn`, but
since the ultimate goal of this feature is to progress towards `service_load`,
it's okay if we only provide information with that context in mind.
##########
docs/connect.html:
##########
@@ -577,7 +638,11 @@ <h4><a id="connect_developing"
href="#connect_developing">Developing a Simple Co
<h5><a id="connect_connectorexample"
href="#connect_connectorexample">Connector Example</a></h5>
- <p>We'll cover the <code>SourceConnector</code> as a simple example.
<code>SinkConnector</code> implementations are very similar. Start by creating
the class that inherits from <code>SourceConnector</code> and add a field that
will store the configuration information to be propagated to the task(s) (the
topic to send data to, and optionally - the filename to read from and the
maximum batch size):</p>
+ <p>We'll cover the <code>SourceConnector</code> as a simple example.
<code>SinkConnector</code> implementations are very similar. Pick a package and
class name, these examples will use the <code>FileStreamSourceConnector</code>
but substitute your own class name where appropriate. In order to <a
href="#connect_plugindiscovery">make the plugin discoverable at runtime</a>,
add a ServiceLoader manifest to your resources in
<code>META-INF/services/org.apache.kafka.connect.source.SourceConnector</code>
with your fully-qualified class name on a single line:</p>
+ <pre class="brush: resource;">
+com.example.FileStreamSourceConnector</pre>
+
+ <p>Create a class that inherits from <code>SourceConnector</code> and add
a field that will store the configuration information to be propagated to the
task(s) (the topic to send data to, and optionally - the filename to read from
and the maximum batch size):</p>
Review Comment:
Worth adding the `package com.example` directive to the `public class
FileStreamSourceConnector ...` code snippet, since the package name serves a
functional purpose now?
##########
docs/connect.html:
##########
@@ -543,6 +543,67 @@ <h6>ACL requirements</h6>
</tbody>
</table>
+ <h4><a id="connect_plugindiscovery" href="#connect_plugindiscovery">Plugin
Discovery</a></h4>
+
+ <p>Plugin discovery is the name for the strategy which the Connect worker
uses to find plugin classes and make them accessible to configure and run in
Connectors and Tasks. This is controlled by the <a
href="#connectconfigs_plugin.discovery"><code>plugin.discovery</code> worker
configuration</a>, and has a significant impact on worker startup time.
<code>SERVICE_LOAD</code> is the fastest strategy, but care should be taken to
verify that plugins are compatible before setting this configuration to
<code>SERVICE_LOAD</code>.</p>
+
+ <p>Prior to version 3.6, this strategy was not configurable, and behaved
like the <code>ONLY_SCAN</code> mode which is compatible with all plugins. For
version 3.6 and later, this mode defaults to <code>HYBRID_WARN</code> which is
also compatible with all plugins, but logs a warning for all plugins which are
incompatible with the other modes. For unit-test environments that use the
<code>EmbeddedConnectCluster</code> this defaults to the
<code>HYBRID_FAIL</code> strategy, which stops the worker with an error if an
incompatible plugin is detected. Finally, the <code>SERVICE_LOAD</code>
strategy will silently hide incompatible plugins and make them unusable.</p>
+
+ <h5><a id="connect_plugindiscovery_compatibility"
href="#connect_plugindiscovery_compatibility">Verifying Plugin
Compatibility</a></h5>
+
+ <p>To verify if all of your plugins are compatible, first ensure that you
are using version 3.6 or later of the Connect runtime. You can then perform one
of the following checks:</p>
+
+ <ul>
+ <li>Start your worker with the default
<code>HYBRID_WARN</code>strategy, and WARN logs enabled for the
<code>org.apache.kafka.connect</code> package. At least one WARN log message
mentioning the <code>plugin.discovery</code> configuration should be printed.
This log message will explicitly say that all plugins are compatible, or list
the incompatible plugins.</li>
+ <li>Start your worker in a test environment with
<code>HYBRID_FAIL</code>. If all plugins are compatible, startup will succeed.
If at least one plugin is not compatible the worker will fail to start up, and
all incompatible plugins will be listed in the exception.</li>
+ </ul>
+
+ <p>If the verification step succeeds, then your current set of installed
plugins are compatible, and it should be safe to change the
<code>plugin.discovery</code> configuration to <code>SERVICE_LOAD</code>. If
you change the set of already-installed plugins, they may no longer be
compatible, and you should repeat the above verification. If the verification
fails, you must address the incompatible plugins before using the
<code>SERVICE_LOAD</code> strategy.</p>
Review Comment:
Ah, gotcha--I think as long as we stick with the semantics for the CLI that
treat classpath plugins differently, this should be fine.
##########
docs/connect.html:
##########
@@ -543,6 +543,67 @@ <h6>ACL requirements</h6>
</tbody>
</table>
+ <h4><a id="connect_plugindiscovery" href="#connect_plugindiscovery">Plugin
Discovery</a></h4>
+
+ <p>Plugin discovery is the name for the strategy which the Connect worker
uses to find plugin classes and make them accessible to configure and run in
Connectors and Tasks. This is controlled by the <a
href="#connectconfigs_plugin.discovery"><code>plugin.discovery</code> worker
configuration</a>, and has a significant impact on worker startup time.
<code>SERVICE_LOAD</code> is the fastest strategy, but care should be taken to
verify that plugins are compatible before setting this configuration to
<code>SERVICE_LOAD</code>.</p>
+
+ <p>Prior to version 3.6, this strategy was not configurable, and behaved
like the <code>ONLY_SCAN</code> mode which is compatible with all plugins. For
version 3.6 and later, this mode defaults to <code>HYBRID_WARN</code> which is
also compatible with all plugins, but logs a warning for all plugins which are
incompatible with the other modes. For unit-test environments that use the
<code>EmbeddedConnectCluster</code> this defaults to the
<code>HYBRID_FAIL</code> strategy, which stops the worker with an error if an
incompatible plugin is detected. Finally, the <code>SERVICE_LOAD</code>
strategy will silently hide incompatible plugins and make them unusable.</p>
Review Comment:
> Some of this is covered in the end of the previous paragraph as a lead-in
to this one; I changed this a bit, but want to avoid repeating myself so I kept
the performance discussion in the first paragraph, and added more specifics
about incompatible plugins to this paragraph.
The issue with this is that it make it seem like the `service_load` mode
only comes with downsides. IMO it's fine to repeat the benefits as long as
we're brief. How does "Finally, although it offers the best performance, the
`service_load` strategy will hide incompatible plugins..." sound?
##########
docs/connect.html:
##########
@@ -543,6 +543,67 @@ <h6>ACL requirements</h6>
</tbody>
</table>
+ <h4><a id="connect_plugindiscovery" href="#connect_plugindiscovery">Plugin
Discovery</a></h4>
+
+ <p>Plugin discovery is the name for the strategy which the Connect worker
uses to find plugin classes and make them accessible to configure and run in
Connectors and Tasks. This is controlled by the <a
href="#connectconfigs_plugin.discovery"><code>plugin.discovery</code> worker
configuration</a>, and has a significant impact on worker startup time.
<code>SERVICE_LOAD</code> is the fastest strategy, but care should be taken to
verify that plugins are compatible before setting this configuration to
<code>SERVICE_LOAD</code>.</p>
+
+ <p>Prior to version 3.6, this strategy was not configurable, and behaved
like the <code>ONLY_SCAN</code> mode which is compatible with all plugins. For
version 3.6 and later, this mode defaults to <code>HYBRID_WARN</code> which is
also compatible with all plugins, but logs a warning for all plugins which are
incompatible with the other modes. For unit-test environments that use the
<code>EmbeddedConnectCluster</code> this defaults to the
<code>HYBRID_FAIL</code> strategy, which stops the worker with an error if an
incompatible plugin is detected. Finally, the <code>SERVICE_LOAD</code>
strategy will silently hide incompatible plugins and make them unusable.</p>
+
+ <h5><a id="connect_plugindiscovery_compatibility"
href="#connect_plugindiscovery_compatibility">Verifying Plugin
Compatibility</a></h5>
+
+ <p>To verify if all of your plugins are compatible, first ensure that you
are using version 3.6 or later of the Connect runtime. You can then perform one
of the following checks:</p>
+
+ <ul>
+ <li>Start your worker with the default
<code>HYBRID_WARN</code>strategy, and WARN logs enabled for the
<code>org.apache.kafka.connect</code> package. At least one WARN log message
mentioning the <code>plugin.discovery</code> configuration should be printed.
This log message will explicitly say that all plugins are compatible, or list
the incompatible plugins.</li>
+ <li>Start your worker in a test environment with
<code>HYBRID_FAIL</code>. If all plugins are compatible, startup will succeed.
If at least one plugin is not compatible the worker will fail to start up, and
all incompatible plugins will be listed in the exception.</li>
+ </ul>
+
+ <p>If the verification step succeeds, then your current set of installed
plugins are compatible, and it should be safe to change the
<code>plugin.discovery</code> configuration to <code>SERVICE_LOAD</code>. If
you change the set of already-installed plugins, they may no longer be
compatible, and you should repeat the above verification. If the verification
fails, you must address the incompatible plugins before using the
<code>SERVICE_LOAD</code> strategy.</p>
+
+ <h5><a id="connect_plugindiscovery_migrateartifact"
href="#connect_plugindiscovery_migrateartifact">Operators: Artifact
Migration</a></h5>
+
+ <p>As an operator of Connect, if you discover incompatible plugins, there
are multiple ways to try to resolve the incompatibility. They are listed below
from most to least preferable.</p>
+
+ <ol>
+ <li>Upgrade your incompatible plugins to the latest release version
from your plugin provider.</li>
+ <li>Contact your plugin provider and request that they migrate the
plugin to be compatible, following the <a
href="#connect_plugindiscovery_migratesource">source migration
instructions</a>, and then upgrade to the migrated version.</li>
+ <li>Migrate the plugin artifacts yourself using the included migration
script.</li>
+ </ol>
+
+ <p>The migration script is located in
<code>bin/connect-plugin-path.sh</code> and
<code>bin\windows\connect-plugin-path.bat</code> of your Kafka installation.
The script can migrate incompatible plugin artifacts already installed on your
Connect worker's <code>plugin.path</code> by adding or modifying JAR or
resource files. This is not suitable for environments using code-signing, as
this may change the artifacts such that they will fail signature verification.
View the built-in help with <code>--help</code>.</p>
+
+ <p>To perform a migration, first use the <code>list</code> subcommand to
get an overview of the plugins available to the script. You must tell the
script where to find plugins, which can be done with the repeatable
<code>--worker-config</code>, <code>--plugin-path</code>, and
<code>--plugin-location</code> arguments. The script will only migrate plugins
present in the paths specified, so if you add plugins to your worker's
classpath, then you will need to specify those plugins via one or more
<code>--plugin-location</code> arguments.</p>
Review Comment:
Hmmm... I agree with the reservations about modifying JAR files in-flight.
Do we have to actually write to those JAR files, though? Could we create/modify
a service loader manifest on the file system instead of inside a JAR file?
I know this is a little inelegant but IMO it's worth considering since it
would reduce the potential for footguns related to classpath plugins and would
increase the general utility of the CLI tool.
##########
docs/connect.html:
##########
@@ -543,6 +543,67 @@ <h6>ACL requirements</h6>
</tbody>
</table>
+ <h4><a id="connect_plugindiscovery" href="#connect_plugindiscovery">Plugin
Discovery</a></h4>
+
+ <p>Plugin discovery is the name for the strategy which the Connect worker
uses to find plugin classes and make them accessible to configure and run in
Connectors and Tasks. This is controlled by the <a
href="#connectconfigs_plugin.discovery"><code>plugin.discovery</code> worker
configuration</a>, and has a significant impact on worker startup time.
<code>SERVICE_LOAD</code> is the fastest strategy, but care should be taken to
verify that plugins are compatible before setting this configuration to
<code>SERVICE_LOAD</code>.</p>
+
+ <p>Prior to version 3.6, this strategy was not configurable, and behaved
like the <code>ONLY_SCAN</code> mode which is compatible with all plugins. For
version 3.6 and later, this mode defaults to <code>HYBRID_WARN</code> which is
also compatible with all plugins, but logs a warning for all plugins which are
incompatible with the other modes. For unit-test environments that use the
<code>EmbeddedConnectCluster</code> this defaults to the
<code>HYBRID_FAIL</code> strategy, which stops the worker with an error if an
incompatible plugin is detected. Finally, the <code>SERVICE_LOAD</code>
strategy will silently hide incompatible plugins and make them unusable.</p>
+
+ <h5><a id="connect_plugindiscovery_compatibility"
href="#connect_plugindiscovery_compatibility">Verifying Plugin
Compatibility</a></h5>
+
+ <p>To verify if all of your plugins are compatible, first ensure that you
are using version 3.6 or later of the Connect runtime. You can then perform one
of the following checks:</p>
+
+ <ul>
+ <li>Start your worker with the default
<code>HYBRID_WARN</code>strategy, and WARN logs enabled for the
<code>org.apache.kafka.connect</code> package. At least one WARN log message
mentioning the <code>plugin.discovery</code> configuration should be printed.
This log message will explicitly say that all plugins are compatible, or list
the incompatible plugins.</li>
+ <li>Start your worker in a test environment with
<code>HYBRID_FAIL</code>. If all plugins are compatible, startup will succeed.
If at least one plugin is not compatible the worker will fail to start up, and
all incompatible plugins will be listed in the exception.</li>
+ </ul>
+
+ <p>If the verification step succeeds, then your current set of installed
plugins are compatible, and it should be safe to change the
<code>plugin.discovery</code> configuration to <code>SERVICE_LOAD</code>. If
you change the set of already-installed plugins, they may no longer be
compatible, and you should repeat the above verification. If the verification
fails, you must address the incompatible plugins before using the
<code>SERVICE_LOAD</code> strategy.</p>
+
+ <h5><a id="connect_plugindiscovery_migrateartifact"
href="#connect_plugindiscovery_migrateartifact">Operators: Artifact
Migration</a></h5>
+
+ <p>As an operator of Connect, if you discover incompatible plugins, there
are multiple ways to try to resolve the incompatibility. They are listed below
from most to least preferable.</p>
+
+ <ol>
+ <li>Upgrade your incompatible plugins to the latest release version
from your plugin provider.</li>
Review Comment:
My intention with the language "Check the latest release" is to imply
searching documentation, release notes, even source code, before installing
that new version onto your Connect worker, which takes more effort from cluster
administrators and introduces the usual risks associated with bumping any
dependency.
##########
docs/connect.html:
##########
@@ -543,6 +543,67 @@ <h6>ACL requirements</h6>
</tbody>
</table>
+ <h4><a id="connect_plugindiscovery" href="#connect_plugindiscovery">Plugin
Discovery</a></h4>
+
+ <p>Plugin discovery is the name for the strategy which the Connect worker
uses to find plugin classes and make them accessible to configure and run in
Connectors and Tasks. This is controlled by the <a
href="#connectconfigs_plugin.discovery"><code>plugin.discovery</code> worker
configuration</a>, and has a significant impact on worker startup time.
<code>SERVICE_LOAD</code> is the fastest strategy, but care should be taken to
verify that plugins are compatible before setting this configuration to
<code>SERVICE_LOAD</code>.</p>
+
+ <p>Prior to version 3.6, this strategy was not configurable, and behaved
like the <code>ONLY_SCAN</code> mode which is compatible with all plugins. For
version 3.6 and later, this mode defaults to <code>HYBRID_WARN</code> which is
also compatible with all plugins, but logs a warning for all plugins which are
incompatible with the other modes. For unit-test environments that use the
<code>EmbeddedConnectCluster</code> this defaults to the
<code>HYBRID_FAIL</code> strategy, which stops the worker with an error if an
incompatible plugin is detected. Finally, the <code>SERVICE_LOAD</code>
strategy will silently hide incompatible plugins and make them unusable.</p>
+
+ <h5><a id="connect_plugindiscovery_compatibility"
href="#connect_plugindiscovery_compatibility">Verifying Plugin
Compatibility</a></h5>
+
+ <p>To verify if all of your plugins are compatible, first ensure that you
are using version 3.6 or later of the Connect runtime. You can then perform one
of the following checks:</p>
+
+ <ul>
+ <li>Start your worker with the default
<code>HYBRID_WARN</code>strategy, and WARN logs enabled for the
<code>org.apache.kafka.connect</code> package. At least one WARN log message
mentioning the <code>plugin.discovery</code> configuration should be printed.
This log message will explicitly say that all plugins are compatible, or list
the incompatible plugins.</li>
+ <li>Start your worker in a test environment with
<code>HYBRID_FAIL</code>. If all plugins are compatible, startup will succeed.
If at least one plugin is not compatible the worker will fail to start up, and
all incompatible plugins will be listed in the exception.</li>
+ </ul>
+
+ <p>If the verification step succeeds, then your current set of installed
plugins are compatible, and it should be safe to change the
<code>plugin.discovery</code> configuration to <code>SERVICE_LOAD</code>. If
you change the set of already-installed plugins, they may no longer be
compatible, and you should repeat the above verification. If the verification
fails, you must address the incompatible plugins before using the
<code>SERVICE_LOAD</code> strategy.</p>
+
+ <h5><a id="connect_plugindiscovery_migrateartifact"
href="#connect_plugindiscovery_migrateartifact">Operators: Artifact
Migration</a></h5>
+
+ <p>As an operator of Connect, if you discover incompatible plugins, there
are multiple ways to try to resolve the incompatibility. They are listed below
from most to least preferable.</p>
+
+ <ol>
+ <li>Upgrade your incompatible plugins to the latest release version
from your plugin provider.</li>
+ <li>Contact your plugin provider and request that they migrate the
plugin to be compatible, following the <a
href="#connect_plugindiscovery_migratesource">source migration
instructions</a>, and then upgrade to the migrated version.</li>
+ <li>Migrate the plugin artifacts yourself using the included migration
script.</li>
+ </ol>
+
+ <p>The migration script is located in
<code>bin/connect-plugin-path.sh</code> and
<code>bin\windows\connect-plugin-path.bat</code> of your Kafka installation.
The script can migrate incompatible plugin artifacts already installed on your
Connect worker's <code>plugin.path</code> by adding or modifying JAR or
resource files. This is not suitable for environments using code-signing, as
this may change the artifacts such that they will fail signature verification.
View the built-in help with <code>--help</code>.</p>
+
+ <p>To perform a migration, first use the <code>list</code> subcommand to
get an overview of the plugins available to the script. You must tell the
script where to find plugins, which can be done with the repeatable
<code>--worker-config</code>, <code>--plugin-path</code>, and
<code>--plugin-location</code> arguments. The script will only migrate plugins
present in the paths specified, so if you add plugins to your worker's
classpath, then you will need to specify those plugins via one or more
<code>--plugin-location</code> arguments.</p>
+
+ <p>Once you see that all incompatible plugins are included in the listing,
you can proceed to dry-run the migration with <code>sync-manifests
--dry-run</code>. This will perform all parts of the migration, except for
writing the results of the migration to disk. Note that the
<code>sync-manifests</code> command requires all specified paths to be
writable, and may alter the contents of the directories. Make a backup of the
specified paths, or copy them to a writable directory.</p>
Review Comment:
Ahh, thanks for enlightening me! I had a different flow in mind where
cluster administrators relied more-heavily on the `list` command to discover
incompatible plugins. If we assume that Connect worker startup is the primary
mechanism for users to discover incompatible plugins, then I think the current
language is better than my suggestion.
> If I change this to `If incompatible plugins are shown` then the
sync-manifests may be incomplete, and the verification steps may fail. I guess
since they should do that verification anyway, having them cross-check the
errors and list output is a bit redundant. WDYT?
I actually really like establishing this expectation. We could add 1-2 extra
sentences instructing users to take note of the list of incompatible plugins
reported by their Connect worker during startup. If we do that, then the
language used here wouldn't really need any modifications since "incompatible
plugins" would clearly reference that list.
##########
docs/connect.html:
##########
@@ -543,6 +543,67 @@ <h6>ACL requirements</h6>
</tbody>
</table>
+ <h4><a id="connect_plugindiscovery" href="#connect_plugindiscovery">Plugin
Discovery</a></h4>
+
+ <p>Plugin discovery is the name for the strategy which the Connect worker
uses to find plugin classes and make them accessible to configure and run in
Connectors and Tasks. This is controlled by the <a
href="#connectconfigs_plugin.discovery"><code>plugin.discovery</code> worker
configuration</a>, and has a significant impact on worker startup time.
<code>SERVICE_LOAD</code> is the fastest strategy, but care should be taken to
verify that plugins are compatible before setting this configuration to
<code>SERVICE_LOAD</code>.</p>
+
+ <p>Prior to version 3.6, this strategy was not configurable, and behaved
like the <code>ONLY_SCAN</code> mode which is compatible with all plugins. For
version 3.6 and later, this mode defaults to <code>HYBRID_WARN</code> which is
also compatible with all plugins, but logs a warning for all plugins which are
incompatible with the other modes. For unit-test environments that use the
<code>EmbeddedConnectCluster</code> this defaults to the
<code>HYBRID_FAIL</code> strategy, which stops the worker with an error if an
incompatible plugin is detected. Finally, the <code>SERVICE_LOAD</code>
strategy will silently hide incompatible plugins and make them unusable.</p>
+
+ <h5><a id="connect_plugindiscovery_compatibility"
href="#connect_plugindiscovery_compatibility">Verifying Plugin
Compatibility</a></h5>
+
+ <p>To verify if all of your plugins are compatible, first ensure that you
are using version 3.6 or later of the Connect runtime. You can then perform one
of the following checks:</p>
+
+ <ul>
+ <li>Start your worker with the default
<code>HYBRID_WARN</code>strategy, and WARN logs enabled for the
<code>org.apache.kafka.connect</code> package. At least one WARN log message
mentioning the <code>plugin.discovery</code> configuration should be printed.
This log message will explicitly say that all plugins are compatible, or list
the incompatible plugins.</li>
+ <li>Start your worker in a test environment with
<code>HYBRID_FAIL</code>. If all plugins are compatible, startup will succeed.
If at least one plugin is not compatible the worker will fail to start up, and
all incompatible plugins will be listed in the exception.</li>
+ </ul>
+
+ <p>If the verification step succeeds, then your current set of installed
plugins are compatible, and it should be safe to change the
<code>plugin.discovery</code> configuration to <code>SERVICE_LOAD</code>. If
you change the set of already-installed plugins, they may no longer be
compatible, and you should repeat the above verification. If the verification
fails, you must address the incompatible plugins before using the
<code>SERVICE_LOAD</code> strategy.</p>
+
+ <h5><a id="connect_plugindiscovery_migrateartifact"
href="#connect_plugindiscovery_migrateartifact">Operators: Artifact
Migration</a></h5>
+
+ <p>As an operator of Connect, if you discover incompatible plugins, there
are multiple ways to try to resolve the incompatibility. They are listed below
from most to least preferable.</p>
+
+ <ol>
+ <li>Upgrade your incompatible plugins to the latest release version
from your plugin provider.</li>
+ <li>Contact your plugin provider and request that they migrate the
plugin to be compatible, following the <a
href="#connect_plugindiscovery_migratesource">source migration
instructions</a>, and then upgrade to the migrated version.</li>
+ <li>Migrate the plugin artifacts yourself using the included migration
script.</li>
+ </ol>
+
+ <p>The migration script is located in
<code>bin/connect-plugin-path.sh</code> and
<code>bin\windows\connect-plugin-path.bat</code> of your Kafka installation.
The script can migrate incompatible plugin artifacts already installed on your
Connect worker's <code>plugin.path</code> by adding or modifying JAR or
resource files. This is not suitable for environments using code-signing, as
this may change the artifacts such that they will fail signature verification.
View the built-in help with <code>--help</code>.</p>
+
+ <p>To perform a migration, first use the <code>list</code> subcommand to
get an overview of the plugins available to the script. You must tell the
script where to find plugins, which can be done with the repeatable
<code>--worker-config</code>, <code>--plugin-path</code>, and
<code>--plugin-location</code> arguments. The script will only migrate plugins
present in the paths specified, so if you add plugins to your worker's
classpath, then you will need to specify those plugins via one or more
<code>--plugin-location</code> arguments.</p>
+
+ <p>Once you see that all incompatible plugins are included in the listing,
you can proceed to dry-run the migration with <code>sync-manifests
--dry-run</code>. This will perform all parts of the migration, except for
writing the results of the migration to disk. Note that the
<code>sync-manifests</code> command requires all specified paths to be
writable, and may alter the contents of the directories. Make a backup of the
specified paths, or copy them to a writable directory.</p>
+
+ <p>Ensure that you have a backup and the dry-run succeeds before removing
the <code>--dry-run</code> flag and actually running the migration. If the
migration fails without the <code>--dry-run</code> flag, then the partially
migrated artifacts should be discarded. The migration is idempotent, so running
it multiple times and on already-migrated plugins is safe. After the migration
is completed, you should <a
href="#connect_plugindiscovery_compatibility">verify the migration is
complete</a>. These migration and verification steps may be put into a
Continuous Integration process to automatically migrate plugins.</p>
+
+ <h5><a id="connect_plugindiscovery_migratesource"
href="#connect_plugindiscovery_migratesource">Developers: Source
Migration</a></h5>
+
+ <p>To make plugins compatible with <code>SERVICE_LOAD</code>, it is
necessary to add <a
href="https://docs.oracle.com/javase/8/docs/api/java/util/ServiceLoader.html";>ServiceLoader</a>
manifests to your source code, which should then be packaged in the release
artifact. Manifests are resource files in <code>META-INF/services/</code> named
after their superclass type, and contain a list of fully-qualified subclass
names, one on each line. Manifests should be located in the same module as the
classes they refer to, not in the corresponding test resources.</p>
Review Comment:
Hmm... I'm leaning slightly towards this sentence being unnecessary, since
we specify earlier that manifests "should then be packaged in the release
artifact."
But, if you want to be explicit about this (which I'm not opposed to), I
think we should frame this more clearly as a warning about a potential footgun;
for example, "Be careful when testing plugin compatibility using the
`hybrid_fail` mode; ensure that the service loader manifest for the plugin is
included in any release artifacts produced for the plugin, instead of only
included in the testing environment for the plugin" (something less wordy would
be nice).
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