Lambda instrumentation implementation

[bonybrown]

Issue #20

Description of changes:

• Adds aws-xray-sdk/lambda.rb to be used in lambda functions to initialise and configure XRay.recorder.
• Adds subclasses of existing Default Context, Emitter and Streamer classes to customise these object's behaviours in the lambda context
• Adds a facade Segment object that the lambda uses as the root segment for all subsegments recorded in the lambda.

This work is based off the implementation of the python xray-sdk for lambda.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license. ✔️

[bonybrown]

Also, created this project that deploys a Lambda function that demonstrates the forked gem.
https://github.com/bonybrown/aws-lambda-ruby-xray-demo

[bonybrown]

All requested changes made and confirmed to be working in https://github.com/bonybrown/aws-lambda-ruby-xray-demo.

[srprash]

Hi @bonybrown ,
Great work. I really appreciate your contribution. I tested the code on my end and also checked out the demo app you put together.
I am experience a little issue with both. When I disable the Active tracing from the lambda function console, I still see an empty trace generated in the X-Ray console. Please see the following images.

And this is the trace data:

Are you seeing this empty trace as well?

[bonybrown]

Just tried, and yes, I'm seeing the same behaviour. Interesting that with Active Tracing disabled in the console, the REPORT output still shows an XRay trace id:

END RequestId: 7238dcbb-84d7-401f-943c-fff00b1c10da
REPORT RequestId: 7238dcbb-84d7-401f-943c-fff00b1c10da	Duration: 259.67 ms	Billed Duration: 300 ms	Memory Size: 128 MB	Max Memory Used: 55 MB	
XRAY TraceId: 1-5d76e4fe-4481878076dd858f6f8c4547	SegmentId:

I'll investigate and get back to you.

[bonybrown]

Hi @srprash - problem identified and fixed. In doing so, identified another problem, now also fixed.
Tested with Active Tracing turned on AND off.
No longer creating empty traces when the lambda is not sampled.

[bonybrown]

Hi @srprash, any update on the progress of this PR? I believe all the issues raised have been addressed.

[srprash]

Hi @bonybrown ,
Sorry for the delay. We are talking to the internal team to see if there's a fix for the localhost entity that we are seeing in the lambda function so that we can avoid the workaround in the PR. Once, it is sorted, we can get this PR merged.

Thanks,
Prashant

[srprash]

Instead of using regex for pattern matching, I think we can fetch the value of AWS_LAMBDA_RUNTIME_API environment variable and check if the req.path begins with this value. I just came across this env variable in lambda runtime and we can avoid using regex matching altogether.

[srprash]

req.path would only give the partial path that does not include the host information. Instead req.uri gives the complete url http://127.0.0.1:9001/...... Doing a start_with? check on req.uri would work better. What do you think?

[bonybrown]

Changed to test against the AWS_LAMBDA_RUNTIME_API environment variable.
Tested in sample app and seems to be working fine.

[srprash]

I keep getting "ERROR -- : can not find the current context." while running the lambda function. Are you getting this too?

[bonybrown]

Sorry, seems that my demo project was using the prior version of aws-xray-sdk-ruby - note to self: it's important to completely remove the vendor directory when changing versions of gems from git.

Have fixed and added tests of begin_segment and begin_subsegment to the demo project.

 # Test begin_segment - should report warning, but not create segment
XRay.recorder.begin_segment 'my_segment'
puts "in segment - begin_segment call should have logged a warning"
# Test end_segment - should report warning
XRay.recorder.end_segment

# Test begin_subsegment, should result in subsegment created
XRay.recorder.begin_subsegment 'sub-segment'
puts "in subsegment"
dynamo_client.list_tables
uri = URI 'https://ip-ranges.amazonaws.com/ip-ranges.json'
http_connection.request(uri).body
XRay.recorder.end_subsegment

Using aws-xray-sdk 0.11.2 from https://github.com/bonybrown/aws-xray-sdk-ruby.git (at lambda-instrumentation@d2d7223) and updated demo project I now get this output:

START RequestId: 7301fb2e-249d-45e7-a468-51167a136a33 Version: $LATEST
W, [2019-10-07T23:45:57.171513 #8]  WARN -- : Cannot create segments inside Lambda function. Returning current segment.
in segment - begin_segment call should have logged a warning
W, [2019-10-07T23:45:57.186110 #8]  WARN -- : Cannot end segment inside Lambda function. Ignored.
in subsegment
END RequestId: 7301fb2e-249d-45e7-a468-51167a136a33
REPORT RequestId: 7301fb2e-249d-45e7-a468-51167a136a33	Duration: 996.39 ms	Billed Duration: 1000 ms	Memory Size: 128 MB	Max Memory Used: 64 MB	Init Duration: 927.05 ms	
XRAY TraceId: 1-5d9bce34-db783d334fd2d50cabd9e15a	SegmentId: 0bc8f498226155ce	Sampled: true	

I don't get ERROR -- : can not find the current context. at all, and attempting to begin a segment results in a warning log message (the existing facade segment is returned) as expected.

[bonybrown]

This is the x-ray trace for the invocation logged above ( TraceId: 1-5d9bce34-db783d334fd2d50cabd9e15a )

[srprash]

Looks good and ready to be merged!
Thanks for your contribution.