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fix(logger): correctly refresh sample rate (#3722)
Co-authored-by: Alexander Schueren <[email protected]>
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Diff for: ‎docs/core/logger.md

+13-86
Original file line numberDiff line numberDiff line change
@@ -805,114 +805,41 @@ You can use values ranging from `0` to `1` (100%) when setting the `sampleRateVa
805805

806806
This feature takes into account transient issues where additional debugging information can be useful.
807807

808-
Sampling decision happens at the Logger initialization. When using the `injectLambdaContext` method either as a decorator or middleware, the sampling decision is refreshed at the beginning of each Lambda invocation for you, except for cold starts.
808+
Sampling decision happens at the Logger initialization. When using the `injectLambdaContext` method either as a decorator or Middy.js middleware, the sampling decision is refreshed at the beginning of each Lambda invocation for you, except for cold starts.
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810810
If you're not using either of these, you'll need to manually call the `refreshSamplingRate()` function at the start of your handler to refresh the sampling decision for each invocation.
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812812
=== "handler.ts"
813813

814-
```typescript hl_lines="6"
814+
```typescript hl_lines="5 9"
815815
--8<-- "examples/snippets/logger/logSampling.ts"
816816
```
817817

818-
=== "Example CloudWatch Logs excerpt - Invocation #1"
818+
1. The log level must be set to a more verbose level than `DEBUG` for log sampling to kick in.
819+
2. You need to call `logger.refreshSamplingRate()` at the start of your handler **only** if you're not using the `injectLambdaContext()` class method decorator or Middy.js middleware.
820+
821+
=== "Example Logs Request #1 (not sampled)"
819822

820823
```json
821-
{
822-
"level": "ERROR",
823-
"message": "This is an ERROR log",
824-
"sampling_rate": "0.5",
825-
"service": "serverlessAirline",
826-
"timestamp": "2021-12-12T22:59:06.334Z",
827-
"xray_trace_id": "abcdef123456abcdef123456abcdef123456"
828-
}
829-
{
830-
"level": "DEBUG",
831-
"message": "This is a DEBUG log that has 50% chance of being printed",
832-
"sampling_rate": "0.5",
833-
"service": "serverlessAirline",
834-
"timestamp": "2021-12-12T22:59:06.337Z",
835-
"xray_trace_id": "abcdef123456abcdef123456abcdef123456"
836-
}
837-
{
838-
"level": "INFO",
839-
"message": "This is an INFO log that has 50% chance of being printed",
840-
"sampling_rate": "0.5",
841-
"service": "serverlessAirline",
842-
"timestamp": "2021-12-12T22:59:06.338Z",
843-
"xray_trace_id": "abcdef123456abcdef123456abcdef123456"
844-
}
845-
{
846-
"level": "WARN",
847-
"message": "This is a WARN log that has 50% chance of being printed",
848-
"sampling_rate": "0.5",
849-
"service": "serverlessAirline",
850-
"timestamp": "2021-12-12T22:59:06.338Z",
851-
"xray_trace_id": "abcdef123456abcdef123456abcdef123456"
852-
}
824+
--8<-- "examples/snippets/logger/samples/debugLogSamplingNotSampled.json"
853825
```
854826

855-
=== "Example CloudWatch Logs excerpt - Invocation #2"
827+
=== "Example Logs Request #2 (sampled)"
856828

857829
```json
858-
{
859-
"level": "ERROR",
860-
"message": "This is an ERROR log",
861-
"sampling_rate": "0.5",
862-
"service": "serverlessAirline",
863-
"timestamp": "2021-12-12T22:59:06.334Z",
864-
"xray_trace_id": "abcdef123456abcdef123456abcdef123456"
865-
}
830+
--8<-- "examples/snippets/logger/samples/debugLogSamplingSampled.json"
866831
```
867832

868-
=== "Example CloudWatch Logs excerpt - Invocation #3"
833+
=== "Example Logs Request #3 (sampled)"
869834

870835
```json
871-
{
872-
"level": "ERROR",
873-
"message": "This is an ERROR log",
874-
"sampling_rate": "0.5",
875-
"service": "serverlessAirline",
876-
"timestamp": "2021-12-12T22:59:06.334Z",
877-
"xray_trace_id": "abcdef123456abcdef123456abcdef123456"
878-
}
879-
{
880-
"level": "DEBUG",
881-
"message": "This is a DEBUG log that has 50% chance of being printed",
882-
"sampling_rate": "0.5",
883-
"service": "serverlessAirline",
884-
"timestamp": "2021-12-12T22:59:06.337Z",
885-
"xray_trace_id": "abcdef123456abcdef123456abcdef123456"
886-
}
887-
{
888-
"level": "INFO",
889-
"message": "This is an INFO log that has 50% chance of being printed",
890-
"sampling_rate": "0.5",
891-
"service": "serverlessAirline",
892-
"timestamp": "2021-12-12T22:59:06.338Z",
893-
"xray_trace_id": "abcdef123456abcdef123456abcdef123456"
894-
}
895-
{
896-
"level": "WARN",
897-
"message": "This is a WARN log that has 50% chance of being printed",
898-
"sampling_rate": "0.5",
899-
"service": "serverlessAirline",
900-
"timestamp": "2021-12-12T22:59:06.338Z",
901-
"xray_trace_id": "abcdef123456abcdef123456abcdef123456"
902-
}
836+
--8<-- "examples/snippets/logger/samples/debugLogSamplingSampled.json"
903837
```
904838

905-
=== "Example CloudWatch Logs excerpt - Invocation #4"
839+
=== "Example Logs Request #4 (not sampled)"
906840

907841
```json
908-
{
909-
"level": "ERROR",
910-
"message": "This is an ERROR log",
911-
"sampling_rate": "0.5",
912-
"service": "serverlessAirline",
913-
"timestamp": "2021-12-12T22:59:06.334Z",
914-
"xray_trace_id": "abcdef123456abcdef123456abcdef123456"
915-
}
842+
--8<-- "examples/snippets/logger/samples/debugLogSamplingNotSampled.json"
916843
```
917844

918845
### Custom Log formatter

Diff for: ‎examples/snippets/logger/logSampling.ts

+7-18
Original file line numberDiff line numberDiff line change
@@ -1,27 +1,16 @@
11
import { Logger } from '@aws-lambda-powertools/logger';
22

3-
// Notice the log level set to 'ERROR'
43
const logger = new Logger({
5-
logLevel: 'ERROR',
4+
logLevel: 'ERROR', // (1)!
65
sampleRateValue: 0.5,
76
});
87

9-
export const handler = async (
10-
_event: unknown,
11-
_context: unknown
12-
): Promise<void> => {
13-
// Refresh sample rate calculation on runtime, only when not using injectLambdaContext
14-
logger.refreshSampleRateCalculation();
15-
// This log item (equal to log level 'ERROR') will be printed to standard output
16-
// in all Lambda invocations
17-
logger.error('This is an ERROR log');
8+
export const handler = async () => {
9+
logger.refreshSampleRateCalculation(); // (2)!
1810

19-
// These log items (below the log level 'ERROR') have ~50% chance
20-
// of being printed in a Lambda invocation
21-
logger.debug('This is a DEBUG log that has 50% chance of being printed');
22-
logger.info('This is an INFO log that has 50% chance of being printed');
23-
logger.warn('This is a WARN log that has 50% chance of being printed');
11+
logger.error('This log is always emitted');
2412

25-
// Optional: refresh sample rate calculation on runtime
26-
// logger.refreshSampleRateCalculation();
13+
logger.debug('This log has ~50% chance of being emitted');
14+
logger.info('This log has ~50% chance of being emitted');
15+
logger.warn('This log has ~50% chance of being emitted');
2716
};

Diff for: ‎examples/snippets/logger/samples/debugLogSamplingNotSampled.json

+8
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,8 @@
1+
{
2+
"level": "ERROR",
3+
"message": "This log is always emitted",
4+
"sampling_rate": "0.5",
5+
"service": "serverlessAirline",
6+
"timestamp": "2021-12-12T22:59:06.334Z",
7+
"xray_trace_id": "abcdef123456abcdef123456abcdef123456"
8+
}

Diff for: ‎examples/snippets/logger/samples/debugLogSamplingSampled.json

+34
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,34 @@
1+
[
2+
{
3+
"level": "ERROR",
4+
"message": "This log is always emitted",
5+
"sampling_rate": "0.5",
6+
"service": "serverlessAirline",
7+
"timestamp": "2021-12-12T22:59:06.334Z",
8+
"xray_trace_id": "abcdef123456abcdef123456abcdef123456"
9+
},
10+
{
11+
"level": "DEBUG",
12+
"message": "This log has ~50% chance of being emitted",
13+
"sampling_rate": "0.5",
14+
"service": "serverlessAirline",
15+
"timestamp": "2021-12-12T22:59:06.337Z",
16+
"xray_trace_id": "abcdef123456abcdef123456abcdef123456"
17+
},
18+
{
19+
"level": "INFO",
20+
"message": "This log has ~50% chance of being emitted",
21+
"sampling_rate": "0.5",
22+
"service": "serverlessAirline",
23+
"timestamp": "2021-12-12T22:59:06.338Z",
24+
"xray_trace_id": "abcdef123456abcdef123456abcdef123456"
25+
},
26+
{
27+
"level": "WARN",
28+
"message": "This log has ~50% chance of being emitted",
29+
"sampling_rate": "0.5",
30+
"service": "serverlessAirline",
31+
"timestamp": "2021-12-12T22:59:06.338Z",
32+
"xray_trace_id": "abcdef123456abcdef123456abcdef123456"
33+
}
34+
]

Diff for: ‎packages/logger/src/Logger.ts

+46-14
Original file line numberDiff line numberDiff line change
@@ -140,7 +140,9 @@ class Logger extends Utility implements LoggerInterface {
140140
/**
141141
* Standard attributes managed by Powertools that will be logged in all log items.
142142
*/
143-
private powertoolsLogData: PowertoolsLogData = <PowertoolsLogData>{};
143+
private powertoolsLogData: PowertoolsLogData = <PowertoolsLogData>{
144+
sampleRateValue: 0,
145+
};
144146
/**
145147
* Temporary log attributes that can be appended with `appendKeys()` method.
146148
*/
@@ -213,6 +215,22 @@ class Logger extends Utility implements LoggerInterface {
213215
*/
214216
#buffer?: CircularMap<string>;
215217

218+
/**
219+
* The debug sampling rate configuration.
220+
*/
221+
readonly #debugLogSampling = {
222+
/**
223+
* The sampling rate value used to determine if the log level should be set to DEBUG.
224+
*/
225+
sampleRateValue: 0,
226+
/**
227+
* The number of times the debug sampling rate has been refreshed.
228+
*
229+
* We use this to determine if we should refresh it again.
230+
*/
231+
refreshedTimes: 0,
232+
};
233+
216234
/**
217235
* Log level used by the current instance of Logger.
218236
*
@@ -302,7 +320,7 @@ class Logger extends Utility implements LoggerInterface {
302320
{
303321
logLevel: this.getLevelName(),
304322
serviceName: this.powertoolsLogData.serviceName,
305-
sampleRateValue: this.powertoolsLogData.sampleRateValue,
323+
sampleRateValue: this.#debugLogSampling.sampleRateValue,
306324
logFormatter: this.getLogFormatter(),
307325
customConfigService: this.getCustomConfigService(),
308326
environment: this.powertoolsLogData.environment,
@@ -547,8 +565,18 @@ class Logger extends Utility implements LoggerInterface {
547565
* This only works for warm starts, because we don't to avoid double sampling.
548566
*/
549567
public refreshSampleRateCalculation(): void {
550-
if (!this.coldStart) {
551-
this.setInitialSampleRate(this.powertoolsLogData.sampleRateValue);
568+
if (this.#debugLogSampling.refreshedTimes === 0) {
569+
this.#debugLogSampling.refreshedTimes++;
570+
return;
571+
}
572+
if (
573+
this.#shouldEnableDebugSampling() &&
574+
this.logLevel > LogLevelThreshold.TRACE
575+
) {
576+
this.setLogLevel('DEBUG');
577+
this.debug('Setting log level to DEBUG due to sampling rate');
578+
} else {
579+
this.setLogLevel(this.getLogLevelNameFromNumber(this.#initialLogLevel));
552580
}
553581
}
554582

@@ -891,6 +919,16 @@ class Logger extends Utility implements LoggerInterface {
891919
}
892920
}
893921

922+
/**
923+
* Make a new debug log sampling decision based on the sample rate value.
924+
*/
925+
#shouldEnableDebugSampling() {
926+
return (
927+
this.#debugLogSampling.sampleRateValue &&
928+
randomInt(0, 100) / 100 <= this.#debugLogSampling.sampleRateValue
929+
);
930+
}
931+
894932
/**
895933
* Check if a given key is reserved and warn the user if it is.
896934
*
@@ -1142,30 +1180,24 @@ class Logger extends Utility implements LoggerInterface {
11421180
* @param sampleRateValue - The sample rate value
11431181
*/
11441182
private setInitialSampleRate(sampleRateValue?: number): void {
1145-
this.powertoolsLogData.sampleRateValue = 0;
11461183
const constructorValue = sampleRateValue;
11471184
const customConfigValue =
11481185
this.getCustomConfigService()?.getSampleRateValue();
11491186
const envVarsValue = this.getEnvVarsService().getSampleRateValue();
11501187
for (const value of [constructorValue, customConfigValue, envVarsValue]) {
11511188
if (this.isValidSampleRate(value)) {
1189+
this.#debugLogSampling.sampleRateValue = value;
11521190
this.powertoolsLogData.sampleRateValue = value;
11531191

11541192
if (
1155-
this.logLevel > LogLevelThreshold.DEBUG &&
1156-
value &&
1157-
randomInt(0, 100) / 100 <= value
1193+
this.#shouldEnableDebugSampling() &&
1194+
this.logLevel > LogLevelThreshold.TRACE
11581195
) {
1159-
// only change logLevel if higher than debug, i.e. don't change from e.g. tracing to debug
11601196
this.setLogLevel('DEBUG');
11611197
this.debug('Setting log level to DEBUG due to sampling rate');
1162-
} else {
1163-
this.setLogLevel(
1164-
this.getLogLevelNameFromNumber(this.#initialLogLevel)
1165-
);
11661198
}
11671199

1168-
return;
1200+
break;
11691201
}
11701202
}
11711203
}

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