Add HTTP semantic convention stability migration guide

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docs/http/migration-guide.md

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+# HTTP semantic convention stability migration guide
+
+Due to the significant number of modifications and the extensive user base
+affected by them, existing HTTP instrumentations published by
+OpenTelemetry are required to implement a migration plan that will assist users in
+transitioning to the stable HTTP semantic conventions.
+
+Specifically, when existing HTTP instrumentations published by OpenTelemetry are
+updated to the stable HTTP semantic conventions, they:
+
+- SHOULD introduce an environment variable `OTEL_SEMCONV_STABILITY_OPT_IN` in
+  their existing major version, which accepts:
+  - `http` - emit the stable HTTP and networking conventions, and stop emitting
+    the old HTTP and networking conventions that the instrumentation emitted
+    previously.
+  - `http/dup` - emit both the old and the stable HTTP and networking
+    conventions, allowing for a phased rollout of the stable semantic
+    conventions.
+  - The default behavior (in the absence of one of these values) is to continue
+    emitting whatever version of the old HTTP and networking conventions the
+    instrumentation was emitting previously.
+- Need to maintain (security patching at a minimum) their existing major version
+  for at least six months after it starts emitting both sets of conventions.
+- May drop the environment variable in their next major version and emit only
+  the stable HTTP and networking conventions.
+
+## Summary of changes
+
+This section summarizes the changes made to the HTTP semantic conventions
+from
+[v1.20.0](https://github.com/open-telemetry/opentelemetry-specification/blob/v1.20.0/specification/trace/semantic_conventions/http.md)
+to
+[v1.23.1 (stable)](https://github.com/open-telemetry/semantic-conventions/blob/v1.23.1/README.md).
+
+### Common attributes across HTTP client and server spans
+
+<!-- prettier-ignore-start -->
+| Change | Comments |
+| --- | --- |
+| `http.method` &rarr; `http.request.method` | Now captures only 9 common HTTP methods by default (configurable) plus `_OTHER` |
+| `http.status_code` &rarr; `http.response.status_code` |  |
+| `http.request.header.<key>` | &bullet; Dash (`"-"`) to underscore (`"_"`) normalization in `<key>` has been removed<br>&bullet; On HTTP server spans: now must be provided to sampler |
+| `http.response.header.<key>` | Dash (`"-"`) to underscore (`"_"`) normalization in `<key>` has been removed |
+| `http.request_content_length` &rarr; `http.request.body.size` | &bullet; Recommended &rarr; Opt-In<br>&bullet; _Not marked stable yet_ |
+| `http.response_content_length` &rarr; `http.response.body.size` | &bullet; Recommended &rarr; Opt-In<br>&bullet; _Not marked stable yet_ |
+| `user_agent.original` | &bullet; On HTTP client spans: Recommended &rarr; Opt-In<br>&bullet; On HTTP server spans: now must be provided to sampler<br>&bullet; See note if [migrating from <= v1.18.0](#migrating-from--v1180) |
+| `net.protocol.name` &rarr; `network.protocol.name` | Recommended &rarr; Conditionally required if not `http` and `network.protocol.version` is set |
+| `net.protocol.version` &rarr; `network.protocol.version` | &bullet; Examples fixed: `2.0` &rarr; `2` and `3.0` &rarr; `3`<br>&bullet; See note if [migrating from <= v1.19.0](#migrating-from--v1190) |
+| `net.sock.family` | Removed |
+| `net.sock.peer.addr` &rarr; `network.peer.address` | On HTTP server spans: if `http.client_ip` was unknown, then also `net.sock.peer.addr` &rarr; `client.address`; `client.address` must be provided to sampler |
+| `net.sock.peer.port` &rarr; `network.peer.port` | Now captured even if same as `server.port` |
+| `net.sock.peer.name` | Removed |
+| New: `http.request.method_original` | Only captured when `http.request.method` is `_OTHER` |
+| New: `error.type` |  |
+<!-- prettier-ignore-end -->
+
+References:
+
+- [Common attributes v1.20.0](https://github.com/open-telemetry/opentelemetry-specification/blob/v1.20.0/specification/trace/semantic_conventions/http.md#common-attributes)
+- [Common attributes v1.23.1 (stable)](https://github.com/open-telemetry/semantic-conventions/blob/v1.23.1/docs/http/http-spans.md#common-attributes)
+
+### HTTP client span attributes
+
+<!-- prettier-ignore-start -->
+| Change | Comments |
+| --- | --- |
+| `http.url` &rarr; `url.full` | |
+| `http.resend_count` &rarr; `http.request.resend_count` | |
+| `net.peer.name` &rarr; `server.address` | |
+| `net.peer.port` &rarr; `server.port` | Now captured even when same as default port for scheme |
+<!-- prettier-ignore-end -->
+
+References:
+
+- [HTTP client span attributes v1.20.0](https://github.com/open-telemetry/opentelemetry-specification/blob/v1.20.0/specification/trace/semantic_conventions/http.md#http-client)
+- [HTTP client span attributes v1.23.1 (stable)](https://github.com/open-telemetry/semantic-conventions/blob/v1.23.1/docs/http/http-spans.md#metric-httpserverrequestduration)
+
+### HTTP server span attributes
+
+<!-- prettier-ignore-start -->
+| Change | Comments |
+| --- | --- |
+| `http.route` | No change |
+| `http.target` &rarr; `url.path` and `url.query` | Split into two separate attributes |
+| `http.scheme` &rarr; `url.scheme` | Now factors in [X-Forwarded-Proto][], [Forwarded#proto][] headers |
+| `http.client_ip` &rarr; `client.address` | If `http.client_ip` was unknown (i.e., no [X-Forwarded-For][], [Forwarded#for][] headers), then `net.sock.peer.addr` &rarr; `client.address`; now must be provided to sampler |
+| `net.host.name` &rarr; `server.address` | Now based only on [Host][Host header], [:authority][HTTP/2 authority], [X-Forwarded-Host][], [Forwarded#host][] headers |
+| `net.host.port` &rarr; `server.port` | Now based only on [Host][Host header], [:authority][HTTP/2 authority], [X-Forwarded-Host][X-Forwarded-Host], [Forwarded#host][] headers |
+<!-- prettier-ignore-end -->
+
+References:
+
+- [HTTP server span attributes v1.20.0](https://github.com/open-telemetry/opentelemetry-specification/blob/v1.20.0/specification/trace/semantic_conventions/http.md#http-server)
+- [HTTP server span attributes v1.23.1 (stable)](https://github.com/open-telemetry/semantic-conventions/blob/v1.23.1/docs/http/http-spans.md#metric-httpserverrequestduration)
+
+### HTTP client and server span names
+
+The `{http.method}` portion of span names is replace by `HTTP` when
+`{http.method}` is `_OTHER`.
+
+See note if [migrating from `<= v1.17.0`](#migrating-from--v1170).
+
+References:
+
+- [HTTP client and server span names v1.20.0](https://github.com/open-telemetry/opentelemetry-specification/blob/v1.20.0/specification/trace/semantic_conventions/http.md#name)
+- [HTTP client and server span names v1.23.1 (stable)](https://github.com/open-telemetry/semantic-conventions/blob/v1.23.1/docs/http/http-spans.md#metric-httpserverrequestduration)
+
+### HTTP client duration metric
+
+Metric changes:
+
+- **Name**: `http.client.duration` &rarr; `http.client.request.duration`
+- **Unit**: `ms` &rarr; `s`
+- **Description**: `Measures the duration of inbound HTTP requests.` &rarr;
+  `Duration of HTTP server requests.`
+- **Histogram buckets**: boundaries updated to reflect change from milliseconds
+  to seconds, and zero bucket boundary removed
+- **Attributes**: see table below
+
+<!-- prettier-ignore-start -->
+| Attribute change | Comments |
+| --- | --- |
+| `http.method` &rarr; `http.request.method` | Now captures only 9 common HTTP methods by default plus `_OTHER` |
+| `http.status_code` &rarr; `http.response.status_code` |  |
+| `net.peer.name` &rarr; `server.address` |  |
+| `net.peer.port` &rarr; `server.port` | Now captured even when same as default port for scheme |
+| `net.sock.peer.addr` | Removed |
+| `net.protocol.name` &rarr; `network.protocol.name` | Recommended &rarr; Conditionally required if not `http` and `network.protocol.version` is set |
+| `net.protocol.version` &rarr; `network.protocol.version` | Examples fixed: `2.0` &rarr; `2` and `3.0` &rarr; `3`; see note if [migrating from `<= v1.19.0`](#migrating-from--v1190) |
+| New: `error.type` |  |
+<!-- prettier-ignore-end -->
+
+References:
+
+- [Metric `http.client.duration` v1.20.0](https://github.com/open-telemetry/opentelemetry-specification/blob/v1.20.0/specification/metrics/semantic_conventions/http-metrics.md#metric-httpclientduration)
+- [Metric `http.client.request.duration` v1.23.1 (stable)](https://github.com/open-telemetry/semantic-conventions/blob/v1.23.1/docs/http/http-metrics.md#metric-httpserverrequestduration)
+
+### HTTP server duration metric
+
+Metric changes:
+
+- **Name**: `http.server.duration` &rarr; `http.server.request.duration`
+- **Unit**: `ms` &rarr; `s`
+- **Description**: `Measures the duration of inbound HTTP requests.` &rarr;
+  `Duration of HTTP server requests.`
+- **Histogram buckets**: boundaries updated to reflect change from milliseconds
+  to seconds, and zero bucket boundary removed
+- **Attributes**: see table below
+
+<!-- prettier-ignore-start -->
+| Attribute change | Comments |
+| --- | --- |
+| `http.route` | No change |
+| `http.method` → `http.request.method` | Now captures only 9 common HTTP methods by default plus `_OTHER` |
+| `http.status_code` → `http.response.status_code` |  |
+| `http.scheme` → `url.scheme` | Now factors in [`X-Forwarded-Proto` span][X-Forwarded-Proto], [`Forwarded#proto` span][Forwarded#proto] headers |
+| `net.protocol.name` → `network.protocol.name` | Recommended → Conditionally required if not `http` and `network.protocol.version` is set |
+| `net.protocol.version` → `network.protocol.version` | Examples fixed: `2.0` → `2` and `3.0` → `3`; see note if [migrating from `<= v1.19.0`](#migrating-from--v1190) |
+| `net.host.name` → `server.address` | &bullet; Recommended → Opt-In (due to high-cardinality vulnerability since based on HTTP headers)<br>&bullet; Now based only on [`Host` span][Host header], [`:authority` span][HTTP/2 authority], [`X-Forwarded-Host` span][X-Forwarded-Host], [`Forwarded#host` span][Forwarded#host] headers |
+| `net.host.port` → `server.port` | &bullet; Recommended → Opt-In (due to high-cardinality vulnerability since based on HTTP headers)<br>&bullet; Now based only on [`Host` span][Host header], [`:authority` span][HTTP/2 authority], [`X-Forwarded-Host` span][X-Forwarded-Host], [`Forwarded#host` span][Forwarded#host] headers |
+| New: `error.type` |  |
+<!-- prettier-ignore-end -->
+
+References:
+
+- [Metric `http.server.duration` v1.20.0](https://github.com/open-telemetry/opentelemetry-specification/blob/v1.20.0/specification/metrics/semantic_conventions/http-metrics.md#metric-httpserverduration)
+- [Metric `http.server.request.duration` v1.23.1 (stable)](https://github.com/open-telemetry/semantic-conventions/blob/v1.23.1/docs/http/http-metrics.md#metric-httpserverrequestduration)
+
+## Migrating from a version prior to v1.20.0?
+
+In addition to the changes made to the HTTP semantic conventions
+from
+[v1.20.0](https://github.com/open-telemetry/opentelemetry-specification/blob/v1.20.0/specification/trace/semantic_conventions/http.md)
+to
+[v1.23.1 (stable)](https://github.com/open-telemetry/semantic-conventions/blob/v1.23.1/README.md),
+there are additional changes if you are migrating to v1.23.1 from a version prior to v1.20.0.
+
+### Migrating from `<= v1.19.0`
+
+- `http.flavor` &rarr; `network.protocol.version`
+  - Examples fixed: `2.0` &rarr; `2` and `3.0` &rarr; `3`
+
+### Migrating from `<= v1.18.0`
+
+- `http.user_agent` &rarr; `user_agent.original`
+
+### Migrating from `<= v1.17.0`
+
+#### HTTP server span name
+
+- When `http.route` is available:<br> `{http.route}` &rarr;
+  `{summary} {http.route}`
+- When `http.route` is not available:<br> `HTTP {http.method}` &rarr;
+  `{summary}`
+
+Where `{summary}` is `{http.method}`, unless `{http.method}` is `_OTHER`, in
+which case `{summary}` is `HTTP`.
+
+#### HTTP client span name
+
+- `HTTP {http.method}` &rarr; `{summary}`
+
+Where `{summary}` is `{http.method}`, unless `{http.method}` is `_OTHER`, in
+which case `{summary}` is `HTTP`.
+
+### Migrating from `<= v1.16.0`
+
+This document does not cover these versions.
+
+[Host header]: https://tools.ietf.org/html/rfc7230#section-5.4
+[HTTP/2 authority]: https://tools.ietf.org/html/rfc9113#section-8.3.1
+[Forwarded#for]:
+https://developer.mozilla.org/docs/Web/HTTP/Headers/Forwarded#for
+[Forwarded#proto]:
+https://developer.mozilla.org/docs/Web/HTTP/Headers/Forwarded#proto
+[Forwarded#host]:
+https://developer.mozilla.org/docs/Web/HTTP/Headers/Forwarded#host
+[X-Forwarded-For]:
+https://developer.mozilla.org/docs/Web/HTTP/Headers/X-Forwarded-For
+[X-Forwarded-Proto]:
+https://developer.mozilla.org/docs/Web/HTTP/Headers/X-Forwarded-Proto
+[X-Forwarded-Host]:
+https://developer.mozilla.org/docs/Web/HTTP/Headers/X-Forwarded-Host