copy edits from elastic/docs-content#827 (#16304)

Author: colleenmcginnis

docs/release-notes/breaking-changes.md

@@ -1,35 +1,33 @@
 ---
-navigation_title: "Elastic APM"
+navigation_title: "Breaking changes"
 ---
 
 # Elastic APM breaking changes
 
-Before you upgrade, carefully review the Elastic APM breaking changes and take the necessary steps to mitigate any issues.
-
-% To learn how to upgrade, check out <uprade docs>.
-
-% ## Next version
+Breaking changes can impact your Elastic applications, potentially disrupting normal operations. Before you upgrade, carefully review the Elastic APM breaking changes and take the necessary steps to mitigate any issues. To learn how to upgrade, check [Upgrade](docs-content://deploy-manage/upgrade.md).
 
+% ## Next version [next-version]
 % **Release date:** Month day, year
 
 % ::::{dropdown} Title of breaking change
 % Description of the breaking change.
 % For more information, check [PR #](PR link).
+
 % **Impact**<br> Impact of the breaking change.
+
 % **Action**<br> Steps for mitigating deprecation impact.
 % ::::
 
 ## 9.0.0 [9-0-0]
-
-**Release date:** March 25, 2025
+**Release date:** April 2, 2025
 
 ::::{dropdown} Change server information endpoint "/" to only accept GET and HEAD requests
 This will surface any agent misconfiguration causing data to be sent to `/` instead of the correct endpoint (for example, `/v1/traces` for OTLP/HTTP).
-For more information, check [PR #15976](https://github.com/elastic/apm-server/pull/15976).
+For more information, check [#15976]({{apm-pull}}15976).
 
-**Impact**<br>Any methods other than `GET` and `HEAD` to `/` will return HTTP 405 Method Not Allowed.
+**Impact**<br> Any methods other than `GET` and `HEAD` to `/` will return HTTP 405 Method Not Allowed.
 
-**Action**<br>Update any existing usage, for example, update `POST /` to `GET /`.
+**Action**<br> Update any existing usage, for example, update `POST /` to `GET /`.
 ::::
 
 ::::{dropdown} The Elasticsearch apm_user role has been removed

docs/release-notes/deprecations.md

@@ -1,14 +1,13 @@
 ---
-navigation_title: "Elastic APM"
+navigation_title: "Deprecations"
 ---
 
 # Elastic APM deprecations
+Over time, certain Elastic functionality becomes outdated and is replaced or removed. To help with the transition, Elastic deprecates functionality for a period before removal, giving you time to update your applications.
 
-Review the deprecated functionality for your Elastic APM version. While deprecations have no immediate impact, we strongly encourage you update your implementation after you upgrade.
+Review the deprecated functionality for Elastic APM. While deprecations have no immediate impact, we strongly encourage you update your implementation after you upgrade. To learn how to upgrade, check out [Upgrade](docs-content://deploy-manage/upgrade.md).
 
-% To learn how to upgrade, check out <uprade docs>.
-
-% ## Next version
+% ## Next version [next-version]
 % **Release date:** Month day, year
 
 % ::::{dropdown} Deprecation title
@@ -19,7 +18,7 @@ Review the deprecated functionality for your Elastic APM version. While deprecat
 % ::::
 
 % ## 9.0.0 [9-0-0]
-% **Release date:** March 25, 2025
+% **Release date:** April 2, 2025
 
 % ::::{dropdown} Deprecation title
 % Description of the deprecation.

docs/release-notes/index.md

@@ -22,8 +22,7 @@ To check for security updates, go to [Security announcements for the Elastic sta
 % ### Fixes [elastic-apm-next-fixes]
 
 ## 9.0.0 [9-0-0]
-
-**Release date:** March 25, 2025
+**Release date:** April 2, 2025
 
 ### Features and enhancements [9-0-0-features-enhancements]
 

docs/release-notes/known-issues.md

@@ -2,27 +2,24 @@
 mapped_pages:
   - https://www.elastic.co/guide/en/observability/current/apm-known-issues.html
 
-navigation_title: "Elastic APM"
+navigation_title: "Known issues"
 ---
 
 # Elastic APM known issues
+Known issues are significant defects or limitations that may impact your implementation. These issues are actively being worked on and will be addressed in a future release. Review the Elastic APM known issues to help you make informed decisions, such as upgrading to a new version.
 
 % Use the following template to add entries to this page.
 
 % :::{dropdown} Title of known issue
-% **Details**
-% On [Month/Day/Year], a known issue was discovered that [description of known issue].
+% **Applicable versions for the known issue and the version for when the known issue was fixed**
+% On [Month Day, Year], a known issue was discovered that [description of known issue].
+% For more information, check [Issue #](Issue link).
 
 % **Workaround**
 % Workaround description.
 
-% **Resolved**
-% On [Month/Day/Year], this issue was resolved.
-
 :::
 
-APM has the following known issues:
-
 :::{dropdown} prefer_ilm required in component templates to create custom lifecycle policies
 
 *Elastic Stack versions: 8.15.1+*
@@ -65,6 +62,7 @@ POST /metrics-apm.transaction.1m-default/_rollover
 POST /metrics-apm.transaction.10m-default/_rollover
 POST /metrics-apm.transaction.60m-default/_rollover
 ```
+
 :::
 
 :::{dropdown} Upgrading to v8.15.0 may cause APM indices to lose their lifecycle policy
@@ -91,10 +89,10 @@ Upgrading to 8.15.1 resolves the lifecycle issue for any new indices created for
 Default `<data_retention_period>` for each data stream is available in [this guide](docs-content://solutions/observability/apps/index-lifecycle-management.md).
 
 This issue is fixed in 8.15.1 ([elastic/elasticsearch#112432](https://github.com/elastic/elasticsearch/pull/112432)).
+
 :::
 
 :::{dropdown} Upgrading to v8.13.0 to v8.13.2 breaks APM anomaly rules [broken-apm-anomaly-rule]
-
 *Elastic Stack versions: 8.13.0, 8.13.1, 8.13.2*<br> *Fixed in Elastic Stack version 8.13.3*
 
 This issue occurs when upgrading the Elastic Stack to version 8.13.0, 8.13.1, or 8.13.2. This issue may go unnoticed unless you actively monitor your {{kib}} logs. The following log indicates the presence of this issue:
@@ -217,7 +215,6 @@ There are three ways to fix this error:
 :::
 
 :::{dropdown} Upgrading APM Server to 8.11+ might break event intake from older APM Java agents
-
 *APM Server versions: >=8.11.0*<br> *Elastic APM Java agent versions: < 1.43.0*
 
 If you are using APM Server (> v8.11.0) and the Elastic APM Java agent (< v1.43.0), the agent may be sending empty histogram metricsets.
@@ -231,7 +228,6 @@ The fix is to upgrade the Elastic APM Java agent to a version >= 1.43.0. Find de
 :::
 
 :::{dropdown} traces-apm@custom ingest pipeline applied to certain data streams unintentionally
-
 *APM Server versions: 8.12.0*<br>
 
 If you’re using the Elastic APM Server v8.12.0, the `traces-apm@custom` ingest pipeline is now additionally applied to data streams `traces-apm.sampled-*` and `traces-apm.rum-*`, and applied twice for `traces-apm-*`. This bug impacts users with a non-empty `traces-apm@custom` ingest pipeline.
@@ -243,7 +239,6 @@ A fix was released in 8.12.1: [elastic/kibana#175448](https://github.com/elastic
 :::
 
 :::{dropdown} Ingesting new JVM metrics in 8.9 and 8.10 breaks upgrade to 8.11 and stops ingestion
-
 *APM Server versions: 8.11.0, 8.11.1*<br> *Elastic APM Java agent versions: 1.39.0+*
 
 If you’re using the Elastic APM Java agent v1.39.0+ to send new JVM metrics to APM Server v8.9.x and v8.10.x, upgrading to 8.11.0 or 8.11.1 will silently fail and stop ingesting APM metrics.
@@ -270,7 +265,6 @@ A fix was released in 8.11.2: [elastic/kibana#171712](https://github.com/elastic
 :::
 
 :::{dropdown} APM integration package upgrade through Fleet causes excessive data stream rollovers
-
 *APM Server versions: <= 8.12.1 +*
 
 If you’re upgrading APM integration package to any versions <= 8.12.1, in some rare cases, the upgrade fails with a mapping conflict error. The upgrade process keeps rolling over the data stream in an unsuccessful attempt to work around the error. As a result, many empty backing indices for APM data streams are created.
@@ -292,8 +286,7 @@ A fix was released in 8.12.2: [elastic/apm-server#12219](https://github.com/elas
 :::
 
 :::{dropdown} Performance regression: APM issues too many small bulk requests for Elasticsearch output
-
-*APM Server versions: >=8.13.0, <= 8.14.2*
+*APM Server versions: >=8.13.0, <= 8.14.2*<br>
 
 If you’re on APM server version >=8.13.0, <= 8.14.2_, using Elasticsearch output, do not specify any `output.elasticsearch.flush_bytes`, and do not disable compression explicitly by setting `output.elasticsearch.compression_level` to `0`, APM server will issue smaller bulk requests of 24KB size, and more bulk requests will need to be made to maintain the original throughput. This causes Elasticsearch to experience higher load, and APM server may exhibit Elasticsearch backpressure symptoms.