feat, docs: support mongoose >=5.7.0 <7

[trentm]

Starting with mongoose 5.7.0, it uses "mongodb" (rather than "mongodb-core") as a backend.

Checklist

• [ ] Figure out why no ".find" spans with mongoose >=5.7.0 (see comment below).
• [ ] Decide if we want to have explicit mongoose tests. Currently we rely on the mongodb-core tests, which I think should still suffice.
• [x] Update documentation
• [ ] Add CHANGELOG.asciidoc entry

[trentm]

Using the examples/trace-mongoose.js in this starter PR I don't get a mongodb span that I expect for a Person.find(...).

For example with [email protected] I see:

% node examples/trace-mongoose.js
...

trace 6b6b2e
`- transaction 7873ce "t1" (65.387ms, outcome=unknown)
   `- span f6a83c "example-trace-mongoose.people.insert" (6.506ms)
   `- span baf633 "example-trace-mongoose.people.find" (0.287ms, sync)
   `- span e8dce2 "admin.$cmd.command" (2.702ms)

However with [email protected]:

% node examples/trace-mongoose.js
...

    trace fa96aa
    `- transaction e23f5c "t1" (64.876ms, outcome=unknown)
       `- span 316ebf "example-trace-mongoose.people.insert" (5.91ms)
       `- span 5d36de "admin.$cmd.endSessions" (1.7095ms)

And with mongoose@6:

% npm ls mongoose
[email protected] /Users/trentm/el/apm-agent-nodejs6
└── [email protected]

% node examples/trace-mongoose.js
...

    trace 26f0e3
    `- transaction dd7638 "t1" (70.447ms, outcome=unknown)
       `- span bbec6d "example-trace-mongoose.people.create" (4ms, sync)
       `- span 2de735 "example-trace-mongoose.people.insert" (2ms, sync)
       `- span 2254d3 "admin.$cmd.endSessions" (0ms, sync)

Where is the ".find" span? Is there a bug in our instrumentation or is this some caching thing in mongoose?

[trentm]

Ah, actually, if I change the script above to:

1. Not delete all entries at the end (so that the DB has one or more Person entries), then
2. Remove the block that adds the "bill" entry, then
3. Re-run.

Now I get a .find span:

    trace 9d9279
    `- transaction 4ff4c9 "t1" (66.033ms, outcome=unknown)
       `- span 2498be "example-trace-mongoose.people.create" (3ms, sync)
       `- span c8c237 "example-trace-mongoose.people.find" (2ms, sync)
       `- span 593382 "admin.$cmd.endSessions" (0ms, sync)

I don't think it is the Mongoose client caching a write and avoiding hitting the DB. Perhaps it is some pipelining or bulk query or transaction where that ".insert" is actually doing the find query as well? Seems unlikely.

There is still something going on in the DB client I don't understand.

[apmmachine]

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• Start Time: 2022-01-25T21:25:58.205+0000

• Duration: 21 min 58 sec

• Commit: 2db939aa372df3a0c67236feff3beffc1e631ffd

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Test	Results
Failed	0
Passed	243005
Skipped	0
Total	243005

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[trentm]

User request for this at https://discuss.elastic.co/t/support-for-mongoose-version-5-7/305849

[aniketbiprojit]

I am confused why mongoose@^6.7.2 isn't supported. I am using 6.8.3 and it internally uses [email protected] which should be supported as per this.

Is there a flag or something that needs to be enabled?

[trentm]

@aniketbiprojit Some history:

• The <5.7.0 for mongoose was added to that table in the documentation in https://github.com/elastic/apm-agent-nodejs/pull/1375 3 years ago, because at the time it wasn't supported.
• Since then mongodb support was added (https://github.com/elastic/apm-agent-nodejs/pull/1423) which should mean later mongoose versions are supported. At the time the documentation for the supported versions of mongoose were not updated.
• More recently I opened this starter PR to look at bumping that supported version range in the documentation and added an example script to actually test mongoose usage -- because we currently don't directly test mongoose. I ran into some things I don't yet understand (see above comments) and haven't yet had a chance to come back to this.

It looks to me like instrumentation of mongoose versions after v5.7.0 is working, at least partially.

[aniketbiprojit]

I am not seeing any instrumentation response in requests/trace from mongoose@ 6.8.3 ([email protected]) on APM.

I had to create a plugin to use pre and post hooks for meanwhile but this doesn't look like methodology. Also, worried about how this effects the cost of each transaction.

targetSchema.pre(/.*/, preQueryHook);
targetSchema.post(/.*/, postQueryHook);

function preQueryHook() {
  if (this.op === undefined) {
    return;
  }
  this.__span = apmAgent.startSpan(
    `${target.op} on ${target._collection?.collectionName
    } with filter: ${JSON.stringify(
      target._conditions ?? {},
      undefined,
      4,
    )}`,
  );
  const span = this.__span as apm.Span | undefined;
  if (span) {
    span.addLabels({
      filter: JSON.stringify(target._conditions ?? {}, undefined, 4),
      update: JSON.stringify(target._update ?? {}, undefined, 4),
      projection: JSON.stringify(
        target._userProvidedFields ?? {}
      ),
    });

    span.setType('db', 'MongoDB', target.op);
  }
}


function postQueryHook() {
  if (this.__span) {
    this.__span.end();
  }
}

[trentm]

This was handled in https://github.com/elastic/apm-agent-nodejs/pull/3653