open-telemetry · SergeyKanzhelev · Oct 28, 2019 · Sep 27, 2019 · Sep 27, 2019 · Sep 27, 2019
diff --git a/specification/data-semantic-conventions.md b/specification/data-semantic-conventions.md
@@ -21,49 +21,233 @@ This way, the operator will not need to learn specifics of a language and
 telemetry collected from multi-language micro-service can still be easily
 correlated and cross-analyzed.
 
-## HTTP client
+## HTTP
 
-This span type represents an outbound HTTP request.
+This section defines semantic conventions for HTTP client and server Spans.
+They can be used for http and https schemes
+and various HTTP versions like 1.1, 2 and SPDY.
+
+### Name
+
+Given an [RFC 3986](https://tools.ietf.org/html/rfc3986) compliant URI of the form `scheme:[//host[:port]]path[?query][#fragment]`,
+the span name of the span SHOULD be set to the URI path value,
+unless another value that represents the identity of the request and has a lower cardinality can be identified
+(e.g. the route for server spans; see below).
+
+### Status
 
-For a HTTP client span, `SpanKind` MUST be `Client`.
+Implementations MUST set status if the HTTP communication failed
+or an HTTP error status code is returned (e.g. above 3xx).
 
-Given an [RFC 3986](https://www.ietf.org/rfc/rfc3986.txt) compliant URI of the form
-`scheme:[//authority]path[?query][#fragment]`, the span name of the span SHOULD
-be set to the URI path value.
+In the case of an HTTP redirect, the request should normally be considered successful,
+unless the client aborts following redirects due to hitting some limit (redirect loop).
+If following a (chain of) redirect(s) successfully, the Status should be set according to the result of the final HTTP request.
 
-If a framework can identify a value that represents the identity of the request
-and has a lower cardinality than the URI path, this value MUST be used for the span name instead.
+Don't set a status message if the reason can be inferred from `http.status_code` and `http.status_text` already.
+
+| HTTP code               | Span status code      |
+|-------------------------|-----------------------|
+| 100...299               | `Ok`                  |
+| 3xx redirect codes      | `DeadlineExceeded` in case of loop (see above) [1], otherwise `Ok` |
+| 401 Unauthorized ⚠      | `Unauthenticated` ⚠ (Unauthorized actually means unauthenticated according to [RFC 7235][rfc-unauthorized])  |
+| 403 Forbidden           | `PermissionDenied`    |
+| 404 Not Found           | `NotFound`            |
+| 429 Too Many Requests   | `ResourceExhausted`   |
+| Other 4xx code          | `InvalidArgument` [1] |
+| 501 Not Implemented     | `Unimplemented`       |
+| 503 Service Unavailable | `Unavailable`         |
+| 504 Gateway Timeout     | `DeadlineExceeded`    |
+| Other 5xx code          | `InternalError` [1]   |
+| Any status code the client fails to interpret (e.g., 093 or 573) | `UnknownError` |
+
+Note that the items marked with [1] are different from the mapping defined in the [OpenCensus semantic conventions][oc-http-status].
+
+[oc-http-status]: https://github.com/census-instrumentation/opencensus-specs/blob/master/trace/HTTP.md#mapping-from-http-status-codes-to-trace-status-codes
+[rfc-unauthorized]: https://tools.ietf.org/html/rfc7235#section-3.1
+
+### Common Attributes
 
 | Attribute name | Notes and examples                                           | Required? |
 | :------------- | :----------------------------------------------------------- | --------- |
 | `component`    | Denotes the type of the span and needs to be `"http"`. | Yes |
 | `http.method` | HTTP request method. E.g. `"GET"`. | Yes |
-| `http.url` | HTTP URL of this request, represented as `scheme://host:port/path?query#fragment` E.g. `"https://example.com:779/path/12314/?q=ddds#123"`. | Yes |
-| `http.status_code` | [HTTP response status code](https://tools.ietf.org/html/rfc7231). E.g. `200` (integer) | No |
-| `http.status_text` | [HTTP reason phrase](https://www.ietf.org/rfc/rfc2616.txt). E.g. `"OK"` | No |
+| `http.url` | Full HTTP request URL in the form `scheme://host[:port]/path?query[#fragment]`. Usually the fragment is not transmitted over HTTP, but if it is known, it should be included nevertheless. | Defined later. |
+| `http.target` | The full request target as passed in a [HTTP request line][] or equivalent, e.g. `/path/12314/?q=ddds#123"`. | Defined later. |
+| `http.host` | The value of the [HTTP host header][]. When the header is empty or not present, this attribute should be the same. | Defined later. |
+| `http.scheme` | The URI scheme identifying the used protocol: `"http"` or `"https"` | Defined later. |
+| `http.status_code` | [HTTP response status code][]. E.g. `200` (integer) | If and only if one was received/sent. |
+| `http.status_text` | [HTTP reason phrase][]. E.g. `"OK"` | No |
+| `http.flavor` | Kind of HTTP protocol used: `"1.0"`, `"1.1"`, `"2"`, `"SPDY"` or `"QUIC"`. |  No |
 
-## HTTP server
+It is recommended to also use the `peer.*` attributes, especially `peer.ip*`.
 
-This span type represents an inbound HTTP request.
+[HTTP response status code]: https://tools.ietf.org/html/rfc7231#section-6
+[HTTP reason phrase]: https://tools.ietf.org/html/rfc7230#section-3.1.2
+
+### HTTP client
+
+This span type represents an outbound HTTP request.
+
+For an HTTP client span, `SpanKind` MUST be `Client`.
+
+If set, `http.url` must be the originally requested URL,
+before any HTTP-redirects that may happen when executing the request.
+
+One of the following sets of attributes is required (in order of usual preference unless for a particular web client/framework it is known that some other set is preferable for some reason; all strings must be non-empty):
+
+* `http.url`
+* `http.scheme`, `http.host`, `http.target`
+* `http.scheme`, `peer.hostname`, `peer.port`, `http.target`
+* `http.scheme`, `peer.ip`, `peer.port`, `http.target`
+
+Note that in some cases `http.host` might be different
+from the `peer.hostname`
+used to look up the `peer.ip` that is actually connected to.
+In that case it is strongly recommended to set the `peer.hostname` attribute in addition to `http.host`.
+
+For status, the following special cases have canonical error codes assigned:
 
-For a HTTP server span, `SpanKind` MUST be `Server`.
+| Client error                | Trace status code  |
+|-----------------------------|--------------------|
+| DNS resolution failed       | `UnknownError`     |
+| Request cancelled by caller | `Cancelled`        |
+| URL cannot be parsed        | `InvalidArgument`  |
+| Request timed out           | `DeadlineExceeded` |
 
-Given an inbound request for a route (e.g. `"/users/:userID?"` the `name`
-attribute of the span SHOULD be set to this route.
+This is not meant to be an exhaustive list
+but if there is no clear mapping for some error conditions,
+instrumentation developers are encouraged to use `UnknownError`
+and open a PR or issue in the specification repository.
 
-If the route can not be determined, the `name` attribute MUST be set to the [RFC 3986 URI](https://www.ietf.org/rfc/rfc3986.txt) path value.
+### HTTP server
 
-If a framework can identify a value that represents the identity of the request
-and has a lower cardinality than the URI path or route, this value MUST be used for the span name instead.
+To understand the attributes defined in this section, it is helpful to read the "Definitions" subsection.
+
+#### Definitions
+
+This section gives a short summary of some concepts
+in web server configuration and web app deployment
+that are relevant to tracing.
+
+Usually, on a physical host, reachable by one or multiple IP addresses, a single HTTP listener process runs.
+If multiple processes are running, they must listen on distinct TCP/UDP ports so that the OS can route incoming TCP/UDP packets to the right one.
+
+Within a single server process, there can be multiple **virtual hosts**.
+The [HTTP host header][] (in combination with a port number) is normally used to determine to which of them to route incoming HTTP requests.
+
+The host header value that matches some virtual host is called the virtual hosts's **server name**. If there are multiple aliases for the virtual host, one of them (often the first one listed in the configuration) is called the **primary server name**. See for example, the Apache [`ServerName`][ap-sn] or NGINX [`server_name`][nx-sn] directive or the CGI specification on `SERVER_NAME` ([RFC 3875][rfc-servername]).
+In practice the HTTP host header is often ignored when just a single virtual host is configured for the IP.
+
+Within a single virtual host, some servers support the concepts of an **HTTP application**
+(for example in Java, the Servlet JSR defines an application as
+"a collection of servlets, HTML pages, classes, and other resources that make up a complete application on a Web server"
+-- SRV.9 in [JSR 53][];
+in a deployment of a Python application to Apache, the application would be the [PEP 3333][] conformant callable that is configured using the
+[`WSGIScriptAlias` directive][modwsgisetup] of `mod_wsgi`).
+
+An application can be "mounted" under some **application root**
+(also know as *[context root][]* *[context prefix][]*, or *[document base][]*)
+which is a fixed path prefix of the URL that determines to which application a request is routed
+(e.g., the server could be configured to route all requests that go to an URL path starting with `/webshop/`
+at a particular virtual host
+to the `com.example.webshop` web application).
+
+Some servers allow to bind the same HTTP application to multiple `(virtual host, application root)` pairs.
+
+> TODO: Find way to trace HTTP application and application root ([opentelemetry/opentelementry-specification#335][])
+
+[PEP 3333]: https://www.python.org/dev/peps/pep-3333/
+[modwsgisetup]: https://modwsgi.readthedocs.io/en/develop/user-guides/quick-configuration-guide.html
+[context root]: https://docs.jboss.org/jbossas/guides/webguide/r2/en/html/ch06.html
+[context prefix]: https://marc.info/?l=apache-cvs&m=130928191414740
+[document base]: http://tomcat.apache.org/tomcat-5.5-doc/config/context.html
+[rfc-servername]: https://tools.ietf.org/html/rfc3875#section-4.1.14
+[ap-sn]: https://httpd.apache.org/docs/2.4/mod/core.html#servername
+[nx-sn]: http://nginx.org/en/docs/http/ngx_http_core_module.html#server_name
+[JSR 53]: https://jcp.org/aboutJava/communityprocess/maintenance/jsr053/index2.html
+[opentelemetry/opentelementry-specification#335]: https://github.com/open-telemetry/opentelemetry-specification/issues/335
+
+#### Semantic conventions
+
+This span type represents an inbound HTTP request.
+
+For an HTTP server span, `SpanKind` MUST be `Server`.
+
+Given an inbound request for a route (e.g. `"/users/:userID?"`) the `name` attribute of the span SHOULD be set to this route.
+If the route does not include the application root, it SHOULD be prepended to the span name.
+
+If the route cannot be determined, the `name` attribute MUST be set as defined in the general semantic conventions for HTTP.
 
 | Attribute name | Notes and examples                                           | Required? |
 | :------------- | :----------------------------------------------------------- | --------- |
-| `component`    | Denotes the type of the span and needs to be `"http"`. | Yes |
-| `http.method` | HTTP request method. E.g. `"GET"`. | Yes |
-| `http.url` | HTTP URL of this request, represented as `scheme://host:port/path?query#fragment` E.g. `"https://example.com:779/path/12314/?q=ddds#123"`. | Yes |
-| `http.route` | The matched route. E.g. `"/users/:userID?"`. | No |
-| `http.status_code` | [HTTP response status code](https://tools.ietf.org/html/rfc7231). E.g. `200` (integer) | No |
-| `http.status_text` | [HTTP reason phrase](https://www.ietf.org/rfc/rfc2616.txt). E.g. `"OK"` | No |
+| `http.server_name` | The primary server name of the matched virtual host. This should be obtained via configuration. If no such configuration can be obtained, this attribute MUST NOT be set ( `host.name` should be used instead). | [1] |
+| `host.name` | Analogous to `peer.hostname` but for the host instead of the peer. | [1] |
+| `host.port` | Local port. E.g., `80` (integer). Analogous to `peer.port`. | [1] |
+| `http.route` | The matched route (path template). (TODO: Define whether to prepend application root) E.g. `"/users/:userID?"`. | No |
+| `http.client_ip` | The IP address of the original client behind all proxies, if known (e.g. from [X-Forwarded-For][]). Note that this is not necessarily the same as `peer.ip*`, which would identify the network-level peer, which may be a proxy. | No |
+
+[HTTP request line]: https://tools.ietf.org/html/rfc7230#section-3.1.1
+[HTTP host header]: https://tools.ietf.org/html/rfc7230#section-5.4
+[X-Forwarded-For]: https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/X-Forwarded-For
+
+**[1]**: `http.url` is usually not readily available on the server side but would have to be assembled in a cumbersome and sometimes lossy process from other information (see e.g. <https://github.com/open-telemetry/opentelemetry-python/pull/148>).
+It is thus preferred to supply the raw data that *is* available.
+Namely, one of the following sets is required (in order of usual preference unless for a particular web server/framework it is known that some other set is preferable for some reason; all strings must be non-empty):
+
+* `http.scheme`, `http.host`, `http.target`
+* `http.scheme`, `http.server_name`, `host.port`, `http.target`
+* `http.scheme`, `host.name`, `host.port`, `http.target`
+* `http.url`
+
+Of course, more than the required attributes can be supplied, but this is recommended only if they cannot be inferred from the sent ones.
+For example, `http.server_name` has shown great value in practice, as bogus HTTP Host headers occur often in the wild.
+
+It is strongly recommended to set `http.server_name` to allow associating requests with some logical server entity.
+
+### Example
+
+As an example, if a browser request for `https://example.com:8080/webshop/articles/4?s=1` is invoked from a host with IP 192.0.2.4, we may have the following Span on the client side:
+
+Span name: `/webshop/articles/4` (NOTE: This is subject to change, see [open-telemetry/opentelemetry-specification#270][].)
+
+[open-telemetry/opentelemetry-specification#270]: https://github.com/open-telemetry/opentelemetry-specification/issues/270
+
+|   Attribute name   |                                       Value             |
+| :----------------- | :-------------------------------------------------------|
+| `component`        | `"http"`                                                |
+| `http.method`      | `"GET"`                                                 |
+| `http.flavor`      | `"1.1"`                                                 |
+| `http.url`         | `"https://example.com:8080/webshop/articles/4?s=1"`     |
+| `peer.ip4`         | `"192.0.2.5"`                                           |
+| `http.status_code` | `200`                                                   |
+| `http.status_text` | `"OK"`                                                  |
+
+The corresponding server Span may look like this:
+
+Span name: `/webshop/articles/:article_id`.
+
+|   Attribute name   |                      Value                      |
+| :----------------- | :---------------------------------------------- |
+| `component`        | `"http"`                                        |
+| `http.method`      | `"GET"`                                         |
+| `http.flavor`      | `"1.1"`                                         |
+| `http.target`      | `"/webshop/articles/4?s=1"`                     |
+| `http.host`        | `"example.com:8080"`                            |
+| `http.server_name` | `"example.com"`                                 |
+| `host.port`        | `8080`                                          |
+| `http.scheme`      | `"https"`                                       |
+| `http.route`       | `"/webshop/articles/:article_id"`               |
+| `http.status_code` | `200`                                           |
+| `http.status_text` | `"OK"`                                          |
+| `http.client_ip`   | `"192.0.2.4"`                                   |
+| `peer.ip4`         | `"192.0.2.5"` (the client goes through a proxy) |
+
+Note that following the recommendations above, `http.url` is not set in the above example.
+If set, it would be
+`"https://example.com:8080/webshop/articles/4?s=1"`
+but due to `http.scheme`, `http.host` and `http.target` being set, it would be redundant.
+As explained above, these separate values are preferred but if for some reason the URL is available but the other values are not,
+URL can replace `http.scheme`, `http.host` and `http.target`.
 
 ## Databases client calls