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Backend granularity (service.target.*) clarifications #674

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merged 12 commits into from
Oct 3, 2022
Merged

Backend granularity (service.target.*) clarifications #674

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d42311c
Backend granularity (service.target.*) clarifications
trentm Aug 17, 2022
dc82a08
tweak, nest-if-guards for db/message cases
trentm Aug 17, 2022
ea9c4c7
exists-check for 'name' case as well
trentm Aug 17, 2022
5f1197d
add the start of my Q3
trentm Aug 17, 2022
fc95ebd
Merge branch 'main' into trentm/backend-granularity-q
trentm Aug 17, 2022
5df58c6
first mismerge
trentm Aug 17, 2022
bebe220
update composite span.name to be calculated from service.target.*
trentm Sep 9, 2022
de440a0
tweak this description
trentm Sep 9, 2022
d315524
I believe this was a typo, json-specs/span_types.json suggests 'sqlse…
trentm Sep 9, 2022
7992292
this was my Q2, but I accidentally inverted the logic
trentm Sep 9, 2022
80f3782
Update "infer destination.service.resource" logic to be based on serv…
trentm Sep 9, 2022
2a66234
(for Q5) update OTel Bridge compatibility mapping pseudo-code to set …
trentm Sep 9, 2022
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29 changes: 16 additions & 13 deletions specs/agents/tracing-spans-service-target.md
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Expand Up @@ -90,7 +90,7 @@ Because there are a lots of moving pieces, implementation will be split into mul

(2) Value is always sent by APM agents for compatibility, but they SHOULD NOT rely on it internally.

(3) HTTP spans (and a few other spans) can't have their `resource` value inferred on APM server without relying on a
(3) HTTP spans (and a few other spans) can't have their `resource` value inferred on APM server without relying on a
brittle mapping on span `type` and `subtype` and breaking the breakdown metrics where `type` and `subtype` are not available.

## Implementation details
Expand All @@ -104,29 +104,32 @@ This specification assumes that values for `span.type` and `span.subtype` fit th
- `span.context.service.target.type` should have the same value as `span.subtype` and fallback to `span.type`.
- `span.context.service.target.name` depends on the span context attributes

On agents, the following algorithm should be used to infer the values for `span.context.service.target.*` fields.
On agents, the following algorithm should be used to infer the values for `span.context.service.target.*` fields.

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REVIEW NOTE: This section slightly tweaks the pseudo-code to infer context.service.target.* from other span fields to avoid a couple gotchas that I hit:

  1. The if (!service_target.type) check in JavaScript would accidentally override service_target.type if it had explicitly been set to the empty string.
  2. The if (span.context.db.instance) branch was changed to if (span.context.db) to use the DB logic for DB spans even if the span didn't happen to have a "db.instance" set -- which is less surprising and matches the old pseudo-code for inferring destination.service.resource.

```javascript
// span created on agent
span = {};

if (span.isExit) {
service_target = span.context.service.target;

if (!service_target.type) { // infer type from span type & subtype

// use sub-type if provided, fallback on type othewise

if ('type' in service_target) { // If not manually specified, infer type from span type & subtype.
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service_target.type = span.subtype || span.type;
}

if (!service_target.name) { // infer name from span attributes

if (span.context.db.instance) { // database spans
service_target.name = span.context.db.instance;

if ('name' in service_target) { // If not manually specified, infer name from span attributes.

if (span.context.db) { // database spans
if (span.context.db.instance) {
service_target.name = span.context.db.instance;
}
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} else if (span.context.message) { // messaging spans
service_target.name = span.context.message.queue.name
if (span.context.message.queue?.name) {
service_target.name = span.context.message.queue?.name
}

} else if (context.http.url) { // http spans
} else if (context.http?.url) { // http spans
service_target.name = getHostFromUrl(context.http.url);
port = getPortFromUrl(context.http.url);
if (port > 0) {
Expand Down