feat(log)!: intoduce log v2 with OpenTelemetry and slog #25701

technicallyty · 2025-12-16T02:48:51Z

Description

Closes: SDK-430

refactors the log package to add support for OpenTelemetry trace correlation. notable changes:

extended logging interface to add context methods - allows trace correlation.
logging constructor function signature changed
logging options all changed to be more standard i.e. log.With<Option> rather than log.SomeOption
if no opentelemetry configuration is set, we simply use zerolog as we did before.
if an OpenTelemetry configuration is set, we use slog, and all logs are output to console and forwarded to the configured logger provider (otel.yml).
New flag introduced, --log_no_console, to allow logs to ONLY go to otel, not to console. (performance related)
reduced log levels to align with slog. some zerolog levels won't be supported now

…ng-metrics

…gging

codecov · 2026-01-06T18:54:07Z

Codecov Report

❌ Patch coverage is 40.15748% with 304 lines in your changes missing coverage. Please review.
✅ Project coverage is 70.04%. Comparing base (fd82917) to head (0aff0fd).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
log/logger.go	22.94%	225 Missing ⚠️
telemetry/config.go	0.00%	22 Missing ⚠️
log/testing.go	75.32%	19 Missing ⚠️
log/options.go	50.00%	16 Missing ⚠️
server/util.go	70.00%	9 Missing ⚠️
server/cmd/execute.go	0.00%	3 Missing ⚠️
log/writer.go	0.00%	2 Missing ⚠️
client/pruning/main.go	0.00%	1 Missing ⚠️
client/snapshot/export.go	0.00%	1 Missing ⚠️
client/snapshot/restore.go	0.00%	1 Missing ⚠️
... and 5 more

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #25701      +/-   ##
==========================================
- Coverage   70.26%   70.04%   -0.22%     
==========================================
  Files         835      843       +8     
  Lines       54361    55094     +733     
==========================================
+ Hits        38196    38592     +396     
- Misses      16165    16502     +337

Files with missing lines	Coverage Δ
baseapp/abci.go	`86.90% <100.00%> (ø)`
client/flags/flags.go	`81.81% <ø> (ø)`
server/api/server.go	`66.31% <100.00%> (ø)`
client/pruning/main.go	`0.00% <0.00%> (ø)`
client/snapshot/export.go	`0.00% <0.00%> (ø)`
client/snapshot/restore.go	`0.00% <0.00%> (ø)`
log/level.go	`95.00% <97.50%> (ø)`
server/cmt_cmds.go	`0.00% <0.00%> (ø)`
server/start.go	`18.57% <0.00%> (ø)`
testutil/network/network.go	`77.20% <0.00%> (ø)`
... and 8 more

... and 6 files with indirect coverage changes

🚀 New features to boost your workflow:

❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

aljo242 · 2026-01-06T21:57:01Z

log/CHANGELOG.md


 ## [Unreleased]

+* [#25701](https://github.com/cosmos/cosmos-sdk/pull/25701) Introduce log v2, enabling OpenTelemetry logging with slog. The logging interface has been updated to accommodate Context logging methods, which allows correlation of logs with traces.


can we link to the upgrade guide for this?

aljo242 · 2026-01-06T22:01:38Z

log/logger.go

-		opt(&logCfg)
+// newZerologLogger creates a Logger backed by zerolog directly.
+// This is the fast path with zero allocations.
+func newZerologLogger(dst io.Writer, cfg *Config) Logger {


previously we filled out the default config and overrode it. Why are we making this change and should cfg be nullable (a pointer)?

we still do that, it's just pulled up to the top level NewLogger now. ill remove the pointers

aljo242 · 2026-01-06T22:02:44Z

log/level_test.go

 	}
 }

-func TestVerboseMode(t *testing.T) {


did we remove this test accidentally?

yes, adding back in

aljo242 · 2026-01-06T22:04:26Z

log/logger.go

-// Impl returns the underlying zerolog logger.
-// It can be used to use zerolog structured API directly instead of the wrapper.
-func (l zeroLogWrapper) Impl() interface{} {
+func (l *zeroLogWrapper) Impl() interface{} {


should return the concrete type here

this would break the interface

aljo242 · 2026-01-06T22:08:43Z

log/options.go

+	// nil = check LoggerProvider.
+	// true = force enable
+	// false = force disable
+	EnableOTEL *bool


why pointer

i wanted to have presence checking here. if set at all, we know that this was explicitly set with the WithOTEL or WIthoutOTEL options. if unset, we can make a decision based on if they had a provider set in their otel configuration.

on second thought though, perhaps we just enable it if they have otel set at all. not actually sure its useful to have this expression here.

aljo242 · 2026-01-06T22:10:33Z

log/with_test.go

-// this test ensures that when the With and WithContext methods are called,
-// that the log wrapper is properly copied with all of its associated options
-// otherwise, verbose mode will fail
-func TestLoggerWith(t *testing.T) {


seems like this test would be fine to still include?

added back, but removed the wrapper3 case because the return type changed, making that test case invalid.

aljo242 · 2026-01-06T22:11:56Z

server/cmd/execute.go

 	ctx := CreateExecuteContext(context.Background())

-	rootCmd.PersistentFlags().String(flags.FlagLogLevel, zerolog.InfoLevel.String(), "The logging level (trace|debug|info|warn|error|fatal|panic|disabled or '*:<level>,<key>:<level>')")
+	rootCmd.PersistentFlags().String(flags.FlagLogLevel, "info", "The logging level (debug|info|warn|error|disabled or '*:<level>,<key>:<level>')")


can we not use the library values from slog etc or something?

yeah added slog.InfoLevel.String() here instead of "info"

aljo242 · 2026-01-06T22:13:16Z

server/util.go

 		viper.New(),
 		cmtcfg.DefaultConfig(),
-		log.NewLogger(os.Stdout),
+		log.NewLogger("cosmos-sdk", log.WithConsoleWriter(os.Stdout)),


should we define a constant for this name? or a default somehow?

added it to a const block

aljo242 · 2026-01-06T22:15:15Z

simapp/app_di.go

@@ -1,373 +0,0 @@
-//go:build !app_v1


why did this need to be removed (not opposed)

oops. meant to add back after testing.

aaronc added 30 commits October 29, 2025 15:44

feat: add tracing

1cf5e6c

work on otel tracer impl

a207f94

add basic baseapp tracing

ee0bfb3

latest WIP

d5f5ea4

add trace exporter setup

47f83e8

fixes

7fafce3

simapp setup, make tracers wrap loggers

bdba035

add test setup

25e3135

fix shutdown order

5c7e464

block trace nesting

d71f7c1

update metrics config and instrumentation

56b215a

start adding otel metric config

f9ce55c

migrate to pure otel setup

3fff00f

fixes

5077567

add basic metrics

31536b6

add telemetry shutdown hook

c922688

docs, cleanup

ed891cc

WIP on removing go-metrics

f685bd4

Merge branch 'main' of github.com:cosmos/cosmos-sdk into aaronc/traci…

42da2f7

…ng-metrics

setup sim test flag

699f5d3

integrate slog logging

5df2460

update to use official env var

1c84edb

add README.md

46e4bcb

delete spaces

f0c3955

setup TestingMain

7dfb754

update suggested config in README.md

1ce344b

add otel custom config options

edbae92

add otel custom config options

0f8085a

add more instrumentation

03b6069

remove pretty print

c4dbd07

technicallyty added 5 commits January 5, 2026 20:44

use zerolog if otel is not enabled

cdc5ba1

update docs

019dae0

update readme

c310570

tidy mods, replaces, and fix golden test

77a276e

Merge remote-tracking branch 'origin/main' into technicallyty/otel-lo…

a2d77cb

…gging

technicallyty added 4 commits January 6, 2026 10:57

no lint

553512b

lint fix

a6b7d96

fix lint

189b46e

fix lint again...

fcb9067

github-actions bot removed the C:Store label Jan 6, 2026

technicallyty added 5 commits January 6, 2026 11:29

fix options docs

3f39296

update readme

b878d77

update readme

86190db

update upgrading

f14fdca

add comment why we cant use zerolog bridge

c8daf44

technicallyty marked this pull request as ready for review January 6, 2026 19:46

technicallyty requested review from aaronc and aljo242 January 6, 2026 19:51

swift1337 self-requested a review January 6, 2026 19:56

aljo242 reviewed Jan 6, 2026

View reviewed changes

technicallyty added 9 commits January 6, 2026 15:35

reference upgrading in changelog

486d4e8

remove pointers for config

0530ec2

re-add missing test

e33d030

add with_test

e36b09e

use slog info name

b51b61f

const default logger name

79707fd

re-add app_di

f10baa3

re-add flag on app.go

32b68f9

fix import order

0aff0fd


		## [Unreleased]

		* [#25701](https://github.com/cosmos/cosmos-sdk/pull/25701) Introduce log v2, enabling OpenTelemetry logging with slog. The logging interface has been updated to accommodate Context logging methods, which allows correlation of logs with traces.

feat(log)!: intoduce log v2 with OpenTelemetry and slog #25701

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feat(log)!: intoduce log v2 with OpenTelemetry and slog #25701

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technicallyty commented Dec 16, 2025 •

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