Repository: gomods/athens
Pull request #1887 (2023-09-11 22:08:40)

fix(pkg/stash): close etcd sessions
## What is the problem I am trying to address?

Athens creates a new session for each 'Stash' request and then never closes it. The sessions (etcd leases) are consequently held forever and eventually leads to resource exhaustion on the etcd cluster.

## How is the fix applied?

This has been fixed by closing the acquired session at the end of the request.

## What GitHub issue(s) does this PR fix or close?

Fixes: #1886


uhthomas: I've also excluded `(*go.etcd.io/etcd/client/v3/concurrency.Session).Close` from errcheck as there's not really any action which can be taken if a session fails to close - the session and lease should automatically expire.
uhthomas: Question for reviewers: should we also remove the error check from `(*go.etcd.io/etcd/clientv3/concurrency.Mutex).Unlock`? There's not really anything which can be done about it. It may be a bit unfortunate to then return an error just because the mutex didn't unlock, despite successfully stashing the module.
uhthomas: I've made the changes inline with my previous comment, I hope this is okay 😄 
uhthomas: We deployed this change yesterday and have seen significant improvement in both Athens and etcd.

## etcd performance

<img width="1454" alt="Screenshot 2023-09-13 at 16 44 56" src="https://github.com/gomods/athens/assets/9749173/c64214f6-bfc5-4fe2-9d79-3e38d719be87">

<img width="1445" alt="Screenshot 2023-09-13 at 16 44 19" src="https://github.com/gomods/athens/assets/9749173/c36a2ead-89c7-4cb7-8950-13a02d1e8d36">

<img width="1447" alt="Screenshot 2023-09-13 at 16 43 40" src="https://github.com/gomods/athens/assets/9749173/7ec9f37a-33a1-4701-836e-5bb5347fc916">

gRPC filtered by LeaseRevoke:

<img width="1445" alt="Screenshot 2023-09-13 at 16 45 50" src="https://github.com/gomods/athens/assets/9749173/b71a25bd-d5e2-45fa-a19d-6cbdfd94cf61">


## Resource usage

### Athens

<img width="1449" alt="Screenshot 2023-09-13 at 16 33 51" src="https://github.com/gomods/athens/assets/9749173/56d727fc-153b-4d9b-b1d0-2786339f66f2">

<img width="1454" alt="Screenshot 2023-09-13 at 16 39 06" src="https://github.com/gomods/athens/assets/9749173/3cbe2900-3305-4877-b510-5dfd02298474">

### etcd

<img width="1454" alt="Screenshot 2023-09-13 at 16 36 02" src="https://github.com/gomods/athens/assets/9749173/c2b660fe-c19b-465b-9527-b9aaa9e4195b">

<img width="1455" alt="Screenshot 2023-09-13 at 16 37 37" src="https://github.com/gomods/athens/assets/9749173/4de0701a-b93e-43a1-8251-9ea73b250c01">


Patch:
diff --git a/.golangci.yml b/.golangci.yml
index d757d9db..3111c62b 100644
--- a/.golangci.yml
+++ b/.golangci.yml
@@ -6,6 +6,10 @@ linters-settings:
   cyclop:
     max-complexity: 12
     skip-tests: true
+  errcheck:
+    exclude-functions:
+      - (*go.etcd.io/etcd/client/v3/concurrency.Mutex).Unlock
+      - (*go.etcd.io/etcd/client/v3/concurrency.Session).Close
   gofumpt:
     extra-rules: true
 
@@ -50,15 +54,15 @@ linters:
 issues:
   exclude-use-default: false
   exclude:
-    - 'package-comments: should have a package comment'
-    - 'ST1000: at least one file in a package should have a package comment'
-    - 'G204: Subprocess launched with a potential tainted input or cmd arguments'
-    - 'G204: Subprocess launched with variable'
-    - 'G402: TLS MinVersion too low.'
-    - 'const `op` is unused'
+    - "package-comments: should have a package comment"
+    - "ST1000: at least one file in a package should have a package comment"
+    - "G204: Subprocess launched with a potential tainted input or cmd arguments"
+    - "G204: Subprocess launched with variable"
+    - "G402: TLS MinVersion too low."
+    - "const `op` is unused"
   exclude-rules:
     - path: cmd/proxy/main.go
-      text: 'G108: Profiling endpoint is automatically exposed on /debug/pprof'
+      text: "G108: Profiling endpoint is automatically exposed on /debug/pprof"
     - path: pkg/stash/stasher.go
       linters:
         - contextcheck
diff --git a/go.mod b/go.mod
index 1d02f2be..800df4cb 100644
--- a/go.mod
+++ b/go.mod
@@ -26,12 +26,13 @@ require (
 	github.com/lib/pq v1.10.7
 	github.com/minio/minio-go/v6 v6.0.57
 	github.com/mitchellh/go-homedir v1.1.0
-	github.com/sirupsen/logrus v1.6.0
+	github.com/sirupsen/logrus v1.7.0
 	github.com/spf13/afero v1.8.2
-	github.com/stretchr/testify v1.7.0
+	github.com/stretchr/testify v1.8.1
 	github.com/technosophos/moniker v0.0.0-20180509230615-a5dbd03a2245
 	github.com/unrolled/secure v0.0.0-20181221173256-0d6b5bb13069
-	go.etcd.io/etcd/client/v3 v3.5.2
+	go.etcd.io/etcd/client/v3 v3.5.9
+	go.etcd.io/etcd/server/v3 v3.5.9
 	go.mongodb.org/mongo-driver v1.7.1
 	go.opencensus.io v0.23.0
 	golang.org/x/mod v0.8.0
@@ -53,28 +54,36 @@ require (
 	github.com/ajg/form v0.0.0-20160822230020-523a5da1a92f // indirect
 	github.com/apparentlymart/go-textseg v1.0.0 // indirect
 	github.com/beorn7/perks v1.0.1 // indirect
+	github.com/cenkalti/backoff/v4 v4.1.1 // indirect
 	github.com/cespare/xxhash/v2 v2.1.2 // indirect
 	github.com/codegangsta/negroni v1.0.0 // indirect
 	github.com/coreos/go-semver v0.3.0 // indirect
 	github.com/coreos/go-systemd/v22 v22.3.2 // indirect
 	github.com/davecgh/go-spew v1.1.1 // indirect
 	github.com/dgryski/go-rendezvous v0.0.0-20200823014737-9f7001d12a5f // indirect
+	github.com/dustin/go-humanize v1.0.0 // indirect
 	github.com/go-playground/locales v0.12.1 // indirect
 	github.com/go-playground/universal-translator v0.16.0 // indirect
 	github.com/go-stack/stack v1.8.0 // indirect
 	github.com/gogo/protobuf v1.3.2 // indirect
-	github.com/golang/groupcache v0.0.0-20200121045136-8c9f03a8e57e // indirect
+	github.com/golang-jwt/jwt/v4 v4.4.2 // indirect
+	github.com/golang/groupcache v0.0.0-20210331224755-41bb18bfe9da // indirect
 	github.com/golang/protobuf v1.5.2 // indirect
 	github.com/golang/snappy v0.0.3 // indirect
+	github.com/google/btree v1.0.1 // indirect
 	github.com/googleapis/gax-go/v2 v2.1.1 // indirect
 	github.com/gorilla/context v1.1.1 // indirect
+	github.com/gorilla/websocket v1.4.2 // indirect
+	github.com/grpc-ecosystem/go-grpc-middleware v1.3.0 // indirect
+	github.com/grpc-ecosystem/go-grpc-prometheus v1.2.0 // indirect
+	github.com/grpc-ecosystem/grpc-gateway v1.16.0 // indirect
 	github.com/hashicorp/errwrap v1.0.0 // indirect
 	github.com/jmespath/go-jmespath v0.4.0 // indirect
 	github.com/joho/godotenv v1.3.0 // indirect
+	github.com/jonboulle/clockwork v0.2.2 // indirect
 	github.com/json-iterator/go v1.1.11 // indirect
 	github.com/klauspost/compress v1.9.5 // indirect
 	github.com/klauspost/cpuid v1.2.3 // indirect
-	github.com/konsorten/go-windows-terminal-sequences v1.0.3 // indirect
 	github.com/kylelemons/godebug v1.1.0 // indirect
 	github.com/markbates/hmax v1.0.0 // indirect
 	github.com/mattn/go-colorable v0.1.9 // indirect
@@ -94,22 +103,38 @@ require (
 	github.com/prometheus/common v0.26.0 // indirect
 	github.com/prometheus/procfs v0.6.0 // indirect
 	github.com/rogpeppe/go-internal v1.3.0 // indirect
+	github.com/soheilhy/cmux v0.1.5 // indirect
+	github.com/spf13/pflag v1.0.5 // indirect
 	github.com/tinylib/msgp v1.0.2 // indirect
+	github.com/tmc/grpc-websocket-proxy v0.0.0-20201229170055-e5319fda7802 // indirect
 	github.com/uber/jaeger-client-go v2.25.0+incompatible // indirect
 	github.com/xdg-go/pbkdf2 v1.0.0 // indirect
 	github.com/xdg-go/scram v1.0.2 // indirect
 	github.com/xdg-go/stringprep v1.0.2 // indirect
+	github.com/xiang90/probing v0.0.0-20190116061207-43a291ad63a2 // indirect
 	github.com/youmark/pkcs8 v0.0.0-20181117223130-1be2e3e5546d // indirect
 	github.com/zclconf/go-cty v0.0.0-20190426224007-b18a157db9e2 // indirect
-	go.etcd.io/etcd/api/v3 v3.5.2 // indirect
-	go.etcd.io/etcd/client/pkg/v3 v3.5.2 // indirect
+	go.etcd.io/bbolt v1.3.7 // indirect
+	go.etcd.io/etcd/api/v3 v3.5.9 // indirect
+	go.etcd.io/etcd/client/pkg/v3 v3.5.9 // indirect
+	go.etcd.io/etcd/client/v2 v2.305.9 // indirect
+	go.etcd.io/etcd/pkg/v3 v3.5.9 // indirect
+	go.etcd.io/etcd/raft/v3 v3.5.9 // indirect
+	go.opentelemetry.io/contrib/instrumentation/google.golang.org/grpc/otelgrpc v0.25.0 // indirect
+	go.opentelemetry.io/otel v1.0.1 // indirect
+	go.opentelemetry.io/otel/exporters/otlp/otlptrace v1.0.1 // indirect
+	go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracegrpc v1.0.1 // indirect
+	go.opentelemetry.io/otel/sdk v1.0.1 // indirect
+	go.opentelemetry.io/otel/trace v1.0.1 // indirect
+	go.opentelemetry.io/proto/otlp v0.9.0 // indirect
 	go.uber.org/atomic v1.9.0 // indirect
 	go.uber.org/multierr v1.7.0 // indirect
 	go.uber.org/zap v1.21.0 // indirect
-	golang.org/x/crypto v0.0.0-20211108221036-ceb1ce70b4fa // indirect
+	golang.org/x/crypto v0.0.0-20220411220226-7b82a4e95df4 // indirect
 	golang.org/x/net v0.8.0 // indirect
 	golang.org/x/sys v0.6.0 // indirect
 	golang.org/x/text v0.8.0 // indirect
+	golang.org/x/time v0.0.0-20210220033141-f8bda1e9f3ba // indirect
 	golang.org/x/xerrors v0.0.0-20200804184101-5ec99f83aff1 // indirect
 	google.golang.org/appengine v1.6.7 // indirect
 	google.golang.org/genproto v0.0.0-20220211171837-173942840c17 // indirect
@@ -118,5 +143,8 @@ require (
 	gopkg.in/DataDog/dd-trace-go.v1 v1.10.0 // indirect
 	gopkg.in/go-playground/assert.v1 v1.2.1 // indirect
 	gopkg.in/ini.v1 v1.42.0 // indirect
+	gopkg.in/natefinch/lumberjack.v2 v2.0.0 // indirect
+	gopkg.in/yaml.v2 v2.4.0 // indirect
 	gopkg.in/yaml.v3 v3.0.1 // indirect
+	sigs.k8s.io/yaml v1.2.0 // indirect
 )
diff --git a/go.sum b/go.sum
index ecd49958..c52ae779 100644
--- a/go.sum
+++ b/go.sum
@@ -118,6 +118,8 @@ github.com/beorn7/perks v1.0.1/go.mod h1:G2ZrVWU2WbWT9wwq4/hrbKbnv/1ERSJQ0ibhJ6r
 github.com/bsm/go-vlq v0.0.0-20150828105119-ec6e8d4f5f4e/go.mod h1:N+BjUcTjSxc2mtRGSCPsat1kze3CUtvJN3/jTXlp29k=
 github.com/bsm/redislock v0.7.2 h1:jggqOio8JyX9FJBKIfjF3fTxAu/v7zC5mAID9LveqG4=
 github.com/bsm/redislock v0.7.2/go.mod h1:kS2g0Yvlymc9Dz8V3iVYAtLAaSVruYbAFdYBDrmC5WU=
+github.com/cenkalti/backoff/v4 v4.1.1 h1:G2HAfAmvm/GcKan2oOQpBXOd2tT2G57ZnZGWa1PxPBQ=
+github.com/cenkalti/backoff/v4 v4.1.1/go.mod h1:scbssz8iZGpm3xbr14ovlUdkxfGXNInqkPWOWmG2CLw=
 github.com/census-instrumentation/opencensus-proto v0.2.1/go.mod h1:f6KPmirojxKA12rnyqOA5BBL4O983OfeGPqjHWSTneU=
 github.com/cespare/xxhash v1.1.0/go.mod h1:XrSqR1VqqWfGrhpAt58auRo0WTKS1nRRg3ghfAqPWnc=
 github.com/cespare/xxhash/v2 v2.1.1/go.mod h1:VGX0DQ3Q6kWi7AoAeZDth3/j3BFtOZR5XLFGgcrjCOs=
@@ -135,6 +137,7 @@ github.com/cncf/xds/go v0.0.0-20210312221358-fbca930ec8ed/go.mod h1:eXthEFrGJvWH
 github.com/cncf/xds/go v0.0.0-20210805033703-aa0b78936158/go.mod h1:eXthEFrGJvWHgFFCl3hGmgk+/aYT6PnTQLykKQRLhEs=
 github.com/cncf/xds/go v0.0.0-20210922020428-25de7278fc84/go.mod h1:eXthEFrGJvWHgFFCl3hGmgk+/aYT6PnTQLykKQRLhEs=
 github.com/cncf/xds/go v0.0.0-20211011173535-cb28da3451f1/go.mod h1:eXthEFrGJvWHgFFCl3hGmgk+/aYT6PnTQLykKQRLhEs=
+github.com/cockroachdb/datadriven v1.0.2 h1:H9MtNqVoVhvd9nCBwOyDjUEdZCREqbIdCJD93PBm/jA=
 github.com/codegangsta/negroni v1.0.0 h1:+aYywywx4bnKXWvoWtRfJ91vC59NbEhEY03sZjQhbVY=
 github.com/codegangsta/negroni v1.0.0/go.mod h1:v0y3T5G7Y1UlFfyxFn/QLRU4a2EuNau2iZY63YTKWo0=
 github.com/coreos/go-semver v0.3.0 h1:wkHLiw0WNATZnSG7epLsujiMCgPAc9xhjJ4tgnAxmfM=
@@ -148,6 +151,7 @@ github.com/dgrijalva/jwt-go v3.2.0+incompatible h1:7qlOGliEKZXTDg6OTjfoBKDXWrumC
 github.com/dgrijalva/jwt-go v3.2.0+incompatible/go.mod h1:E3ru+11k8xSBh+hMPgOLZmtrrCbhqsmaPHjLKYnJCaQ=
 github.com/dgryski/go-rendezvous v0.0.0-20200823014737-9f7001d12a5f h1:lO4WD4F/rVNCu3HqELle0jiPLLBs70cWOduZpkS1E78=
 github.com/dgryski/go-rendezvous v0.0.0-20200823014737-9f7001d12a5f/go.mod h1:cuUVRXasLTGF7a8hSLbxyZXjz+1KgoB3wDUb6vlszIc=
+github.com/dustin/go-humanize v1.0.0 h1:VSnTsYCnlFHaM2/igO1h6X3HA71jcobQuxemgkq4zYo=
 github.com/dustin/go-humanize v1.0.0/go.mod h1:HtrtbFcZ19U5GC7JDqmcUSB87Iq5E25KnS6fMYU6eOk=
 github.com/envoyproxy/go-control-plane v0.9.0/go.mod h1:YTl/9mNaCwkRvm6d1a2C3ymFceY/DCBVvsKhRF0iEA4=
 github.com/envoyproxy/go-control-plane v0.9.1-0.20191026205805-5f8ba28d4473/go.mod h1:YTl/9mNaCwkRvm6d1a2C3ymFceY/DCBVvsKhRF0iEA4=
@@ -217,11 +221,14 @@ github.com/godbus/dbus/v5 v5.0.4/go.mod h1:xhWf0FNVPg57R7Z0UbKHbJfkEywrmjJnf7w5x
 github.com/gogo/protobuf v1.1.1/go.mod h1:r8qH/GZQm5c6nD/R0oafs1akxWv10x8SbQlK7atdtwQ=
 github.com/gogo/protobuf v1.3.2 h1:Ov1cvc58UF3b5XjBnZv7+opcTcQFZebYjWzi34vdm4Q=
 github.com/gogo/protobuf v1.3.2/go.mod h1:P1XiOD3dCwIKUDQYPy72D8LYyHL2YPYrpS2s69NZV8Q=
+github.com/golang-jwt/jwt/v4 v4.4.2 h1:rcc4lwaZgFMCZ5jxF9ABolDcIHdBytAFgqFPbSJQAYs=
+github.com/golang-jwt/jwt/v4 v4.4.2/go.mod h1:m21LjoU+eqJr34lmDMbreY2eSTRJ1cv77w39/MY0Ch0=
 github.com/golang/glog v0.0.0-20160126235308-23def4e6c14b/go.mod h1:SBH7ygxi8pfUlaOkMMuAQtPIUF8ecWP5IEl/CR7VP2Q=
 github.com/golang/groupcache v0.0.0-20190702054246-869f871628b6/go.mod h1:cIg4eruTrX1D+g88fzRXU5OdNfaM+9IcxsU14FzY7Hc=
 github.com/golang/groupcache v0.0.0-20191227052852-215e87163ea7/go.mod h1:cIg4eruTrX1D+g88fzRXU5OdNfaM+9IcxsU14FzY7Hc=
-github.com/golang/groupcache v0.0.0-20200121045136-8c9f03a8e57e h1:1r7pUrabqp18hOBcwBwiTsbnFeTZHV9eER/QT5JVZxY=
 github.com/golang/groupcache v0.0.0-20200121045136-8c9f03a8e57e/go.mod h1:cIg4eruTrX1D+g88fzRXU5OdNfaM+9IcxsU14FzY7Hc=
+github.com/golang/groupcache v0.0.0-20210331224755-41bb18bfe9da h1:oI5xCqsCo564l8iNU+DwB5epxmsaqB+rhGL0m5jtYqE=
+github.com/golang/groupcache v0.0.0-20210331224755-41bb18bfe9da/go.mod h1:cIg4eruTrX1D+g88fzRXU5OdNfaM+9IcxsU14FzY7Hc=
 github.com/golang/mock v1.1.1/go.mod h1:oTYuIxOrZwtPieC+H1uAHpcLFnEyAGVDL/k47Jfbm0A=
 github.com/golang/mock v1.2.0/go.mod h1:oTYuIxOrZwtPieC+H1uAHpcLFnEyAGVDL/k47Jfbm0A=
 github.com/golang/mock v1.3.1/go.mod h1:sBzyDLLjw3U8JLTeZvSv8jJB+tU5PVekmnlKIyFUx0Y=
@@ -255,6 +262,8 @@ github.com/golang/snappy v0.0.3 h1:fHPg5GQYlCeLIPB9BZqMVR5nR9A+IM5zcgeTdjMYmLA=
 github.com/golang/snappy v0.0.3/go.mod h1:/XxbfmMg8lxefKM7IXC3fBNl/7bRcc72aCRzEWrmP2Q=
 github.com/google/btree v0.0.0-20180813153112-4030bb1f1f0c/go.mod h1:lNA+9X1NB3Zf8V7Ke586lFgjr2dZNuvo3lPJSGZ5JPQ=
 github.com/google/btree v1.0.0/go.mod h1:lNA+9X1NB3Zf8V7Ke586lFgjr2dZNuvo3lPJSGZ5JPQ=
+github.com/google/btree v1.0.1 h1:gK4Kx5IaGY9CD5sPJ36FHiBJ6ZXl0kilRiiCj+jdYp4=
+github.com/google/btree v1.0.1/go.mod h1:xXMiIv4Fb/0kKde4SpL7qlzvu5cMJDRkFDxJfI9uaxA=
 github.com/google/go-cmp v0.2.0/go.mod h1:oXzfMopK8JAjlY9xF4vHSVASa0yLyX7SntLO5aqRK0M=
 github.com/google/go-cmp v0.3.0/go.mod h1:8QqcDgzrUqlUb/G2PQTWiueGozuR1884gddMywk6iLU=
 github.com/google/go-cmp v0.3.1/go.mod h1:8QqcDgzrUqlUb/G2PQTWiueGozuR1884gddMywk6iLU=
@@ -313,7 +322,13 @@ github.com/gorilla/securecookie v1.1.1 h1:miw7JPhV+b/lAHSXz4qd/nN9jRiAFV5FwjeKyC
 github.com/gorilla/securecookie v1.1.1/go.mod h1:ra0sb63/xPlUeL+yeDciTfxMRAA+MP+HVt/4epWDjd4=
 github.com/gorilla/sessions v1.1.3 h1:uXoZdcdA5XdXF3QzuSlheVRUvjl+1rKY7zBXL68L9RU=
 github.com/gorilla/sessions v1.1.3/go.mod h1:8KCfur6+4Mqcc6S0FEfKuN15Vl5MgXW92AE8ovaJD0w=
+github.com/gorilla/websocket v1.4.2 h1:+/TMaTYc4QFitKJxsQ7Yye35DkWvkdLcvGKqM+x0Ufc=
+github.com/gorilla/websocket v1.4.2/go.mod h1:YR8l580nyteQvAITg2hZ9XVh4b55+EU/adAjf1fMHhE=
+github.com/grpc-ecosystem/go-grpc-middleware v1.3.0 h1:+9834+KizmvFV7pXQGSXQTsaWhq2GjuNUt0aUU0YBYw=
+github.com/grpc-ecosystem/go-grpc-middleware v1.3.0/go.mod h1:z0ButlSOZa5vEBq9m2m2hlwIgKw+rp3sdCBRoJY+30Y=
+github.com/grpc-ecosystem/go-grpc-prometheus v1.2.0 h1:Ovs26xHkKqVztRpIrF/92BcuyuQ/YW4NSIpoGtfXNho=
 github.com/grpc-ecosystem/go-grpc-prometheus v1.2.0/go.mod h1:8NvIoxWQoOIhqOTXgfV/d3M/q6VIi02HzZEHgUlZvzk=
+github.com/grpc-ecosystem/grpc-gateway v1.16.0 h1:gmcG1KaJ57LophUzW0Hy8NmPhnMZb4M0+kPpLofRdBo=
 github.com/grpc-ecosystem/grpc-gateway v1.16.0/go.mod h1:BDjrQk3hbvj6Nolgz8mAMFbcEtjT1g+wF4CSlocrBnw=
 github.com/hashicorp/errwrap v0.0.0-20180715044906-d6c0cd880357/go.mod h1:YH+1FKiLXxHSkmPseP+kNlulaMuP3n2brvKWEqk/Jc4=
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@@ -336,6 +351,8 @@ github.com/jmespath/go-jmespath/internal/testify v1.5.1 h1:shLQSRRSCCPj3f2gpwzGw
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@@ -360,15 +377,14 @@ github.com/klauspost/cpuid v1.2.3 h1:CCtW0xUnWGVINKvE/WWOYKdsPV6mawAtvQuSl8guwQs
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@@ -419,6 +435,7 @@ github.com/onsi/gomega v1.7.1/go.mod h1:XdKZgCCFLUoM/7CFJVPcG8C1xQ1AJ0vpAezJrB7J
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@@ -433,7 +450,6 @@ github.com/prometheus/client_golang v0.9.1/go.mod h1:7SWBe2y4D6OKWSNQJUaRYU/AaXP
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@@ -464,33 +480,45 @@ github.com/sirupsen/logrus v1.4.0/go.mod h1:LxeOpSwHxABJmUn/MG1IvRgCAasNZTLOkJPx
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@@ -512,12 +542,22 @@ github.com/yuin/goldmark v1.3.5/go.mod h1:mwnBkeHKe2W/ZEtQ+71ViKU8L12m81fl3OWwC1
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@@ -528,16 +568,32 @@ go.opencensus.io v0.22.4/go.mod h1:yxeiOL68Rb0Xd1ddK5vPZ/oVn4vY4Ynel7k9FzqtOIw=
 go.opencensus.io v0.22.5/go.mod h1:5pWMHQbX5EPX2/62yrJeAkowc+lfs/XD7Uxpq3pI6kk=
 go.opencensus.io v0.23.0 h1:gqCw0LfLxScz8irSi8exQc7fyQ0fKQU/qnC/X8+V/1M=
 go.opencensus.io v0.23.0/go.mod h1:XItmlyltB5F7CS4xOC1DcqMoFqwtC6OG2xF7mCv7P7E=
+go.opentelemetry.io/contrib/instrumentation/google.golang.org/grpc/otelgrpc v0.25.0 h1:Wx7nFnvCaissIUZxPkBqDz2963Z+Cl+PkYbDKzTxDqQ=
+go.opentelemetry.io/contrib/instrumentation/google.golang.org/grpc/otelgrpc v0.25.0/go.mod h1:E5NNboN0UqSAki0Atn9kVwaN7I+l25gGxDqBueo/74E=
+go.opentelemetry.io/otel v1.0.1 h1:4XKyXmfqJLOQ7feyV5DB6gsBFZ0ltB8vLtp6pj4JIcc=
+go.opentelemetry.io/otel v1.0.1/go.mod h1:OPEOD4jIT2SlZPMmwT6FqZz2C0ZNdQqiWcoK6M0SNFU=
+go.opentelemetry.io/otel/exporters/otlp/otlptrace v1.0.1 h1:ofMbch7i29qIUf7VtF+r0HRF6ac0SBaPSziSsKp7wkk=
+go.opentelemetry.io/otel/exporters/otlp/otlptrace v1.0.1/go.mod h1:Kv8liBeVNFkkkbilbgWRpV+wWuu+H5xdOT6HAgd30iw=
+go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracegrpc v1.0.1 h1:CFMFNoz+CGprjFAFy+RJFrfEe4GBia3RRm2a4fREvCA=
+go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracegrpc v1.0.1/go.mod h1:xOvWoTOrQjxjW61xtOmD/WKGRYb/P4NzRo3bs65U6Rk=
+go.opentelemetry.io/otel/sdk v1.0.1 h1:wXxFEWGo7XfXupPwVJvTBOaPBC9FEg0wB8hMNrKk+cA=
+go.opentelemetry.io/otel/sdk v1.0.1/go.mod h1:HrdXne+BiwsOHYYkBE5ysIcv2bvdZstxzmCQhxTcZkI=
+go.opentelemetry.io/otel/trace v1.0.1 h1:StTeIH6Q3G4r0Fiw34LTokUFESZgIDUr0qIJ7mKmAfw=
+go.opentelemetry.io/otel/trace v1.0.1/go.mod h1:5g4i4fKLaX2BQpSBsxw8YYcgKpMMSW3x7ZTuYBr3sUk=
 go.opentelemetry.io/proto/otlp v0.7.0/go.mod h1:PqfVotwruBrMGOCsRd/89rSnXhoiJIqeYNgFYFoEGnI=
+go.opentelemetry.io/proto/otlp v0.9.0 h1:C0g6TWmQYvjKRnljRULLWUVJGy8Uvu0NEL/5frY2/t4=
+go.opentelemetry.io/proto/otlp v0.9.0/go.mod h1:1vKfU9rv61e9EVGthD1zNvUbiwPcimSsOPU9brfSHJg=
+go.uber.org/atomic v1.4.0/go.mod h1:gD2HeocX3+yG+ygLZcrzQJaqmWj9AIm7n08wl/qW/PE=
 go.uber.org/atomic v1.7.0/go.mod h1:fEN4uk6kAWBTFdckzkM89CLk9XfWZrxpCo0nPH17wJc=
 go.uber.org/atomic v1.9.0 h1:ECmE8Bn/WFTYwEW/bpKD3M8VtR/zQVbavAoalC1PYyE=
 go.uber.org/atomic v1.9.0/go.mod h1:fEN4uk6kAWBTFdckzkM89CLk9XfWZrxpCo0nPH17wJc=
 go.uber.org/goleak v1.1.11 h1:wy28qYRKZgnJTxGxvye5/wgWr1EKjmUDGYox5mGlRlI=
 go.uber.org/goleak v1.1.11/go.mod h1:cwTWslyiVhfpKIDGSZEM2HlOvcqm+tG4zioyIeLoqMQ=
+go.uber.org/multierr v1.1.0/go.mod h1:wR5kodmAFQ0UK8QlbwjlSNy0Z68gJhDJUG5sjR94q/0=
 go.uber.org/multierr v1.6.0/go.mod h1:cdWPpRnG4AhwMwsgIHip0KRBQjJy5kYEpYjJxpXp9iU=
 go.uber.org/multierr v1.7.0 h1:zaiO/rmgFjbmCXdSYJWQcdvOCsthmdaHfr3Gm2Kx4Ec=
 go.uber.org/multierr v1.7.0/go.mod h1:7EAYxJLBy9rStEaz58O2t4Uvip6FSURkq8/ppBp95ak=
-go.uber.org/zap v1.17.0/go.mod h1:MXVU+bhUf/A7Xi2HNOnopQOrmycQ5Ih87HtOu4q5SSo=
+go.uber.org/zap v1.10.0/go.mod h1:vwi/ZaCAaUcBkycHslxD9B2zi4UTXhF60s6SWpuDF0Q=
 go.uber.org/zap v1.21.0 h1:WefMeulhovoZ2sYXz7st6K0sLj7bBhpiFaud4r4zST8=
 go.uber.org/zap v1.21.0/go.mod h1:wjWOCqI0f2ZZrJF/UufIOkiC8ii6tm1iqIsLo76RfJw=
 golang.org/x/crypto v0.0.0-20180904163835-0709b304e793/go.mod h1:6SG95UA2DQfeDnfUPMdvaQW0Q7yPrPDi9nlGo2tz2b4=
@@ -553,8 +609,9 @@ golang.org/x/crypto v0.0.0-20200302210943-78000ba7a073/go.mod h1:LzIPMQfyMNhhGPh
 golang.org/x/crypto v0.0.0-20200622213623-75b288015ac9/go.mod h1:LzIPMQfyMNhhGPhUkYOs5KpL4U8rLKemX1yGLhDgUto=
 golang.org/x/crypto v0.0.0-20210421170649-83a5a9bb288b/go.mod h1:T9bdIzuCu7OtxOm1hfPfRQxPLYneinmdGuTeoZ9dtd4=
 golang.org/x/crypto v0.0.0-20210921155107-089bfa567519/go.mod h1:GvvjBRRGRdwPK5ydBHafDWAxML/pGHZbMvKqRZ5+Abc=
-golang.org/x/crypto v0.0.0-20211108221036-ceb1ce70b4fa h1:idItI2DDfCokpg0N51B2VtiLdJ4vAuXC9fnCb2gACo4=
 golang.org/x/crypto v0.0.0-20211108221036-ceb1ce70b4fa/go.mod h1:GvvjBRRGRdwPK5ydBHafDWAxML/pGHZbMvKqRZ5+Abc=
+golang.org/x/crypto v0.0.0-20220411220226-7b82a4e95df4 h1:kUhD7nTDoI3fVd9G4ORWrbV5NY0liEs/Jg2pv5f+bBA=
+golang.org/x/crypto v0.0.0-20220411220226-7b82a4e95df4/go.mod h1:IxCIyHEi3zRg3s0A5j5BB6A9Jmi73HwBIUl50j+osU4=
 golang.org/x/exp v0.0.0-20190121172915-509febef88a4/go.mod h1:CJ0aWSM057203Lf6IL+f9T1iT9GByDxfZKAQTCR3kQA=
 golang.org/x/exp v0.0.0-20190306152737-a1d7652674e8/go.mod h1:CJ0aWSM057203Lf6IL+f9T1iT9GByDxfZKAQTCR3kQA=
 golang.org/x/exp v0.0.0-20190510132918-efd6b22b2522/go.mod h1:ZjyILWgesfNpC6sMxTJOJm9Kp84zZh5NQWvqDGG3Qr8=
@@ -630,6 +687,7 @@ golang.org/x/net v0.0.0-20200822124328-c89045814202/go.mod h1:/O7V0waA8r7cgGh81R
 golang.org/x/net v0.0.0-20201021035429-f5854403a974/go.mod h1:sp8m0HH+o8qH0wwXwYZr8TS3Oi6o0r6Gce1SSxlDquU=
 golang.org/x/net v0.0.0-20201031054903-ff519b6c9102/go.mod h1:sp8m0HH+o8qH0wwXwYZr8TS3Oi6o0r6Gce1SSxlDquU=
 golang.org/x/net v0.0.0-20201110031124-69a78807bb2b/go.mod h1:sp8m0HH+o8qH0wwXwYZr8TS3Oi6o0r6Gce1SSxlDquU=
+golang.org/x/net v0.0.0-20201202161906-c7110b5ffcbb/go.mod h1:sp8m0HH+o8qH0wwXwYZr8TS3Oi6o0r6Gce1SSxlDquU=
 golang.org/x/net v0.0.0-20201209123823-ac852fbbde11/go.mod h1:m0MpNAwzfU5UDzcl9v0D8zg8gWTRqZa9RBIspLL5mdg=
 golang.org/x/net v0.0.0-20201224014010-6772e930b67b/go.mod h1:m0MpNAwzfU5UDzcl9v0D8zg8gWTRqZa9RBIspLL5mdg=
 golang.org/x/net v0.0.0-20210119194325-5f4716e94777/go.mod h1:m0MpNAwzfU5UDzcl9v0D8zg8gWTRqZa9RBIspLL5mdg=
@@ -693,6 +751,7 @@ golang.org/x/sys v0.0.0-20190726091711-fc99dfbffb4e/go.mod h1:h1NjWce9XRLGQEsW7w
 golang.org/x/sys v0.0.0-20190904154756-749cb33beabd/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.0.0-20191001151750-bb3f8db39f24/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.0.0-20191005200804-aed5e4c7ecf9/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
+golang.org/x/sys v0.0.0-20191026070338-33540a1f6037/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.0.0-20191120155948-bd437916bb0e/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.0.0-20191204072324-ce4227a45e2e/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.0.0-20191228213918-04cbcbbfeed8/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
@@ -727,7 +786,6 @@ golang.org/x/sys v0.0.0-20210305230114-8fe3ee5dd75b/go.mod h1:h1NjWce9XRLGQEsW7w
 golang.org/x/sys v0.0.0-20210315160823-c6e025ad8005/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.0.0-20210320140829-1e4c9ba3b0c4/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.0.0-20210330210617-4fbd30eecc44/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
-golang.org/x/sys v0.0.0-20210403161142-5e06dd20ab57/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.0.0-20210423082822-04245dca01da/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.0.0-20210423185535-09eb48e85fd7/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.0.0-20210510120138-977fb7262007/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
@@ -768,6 +826,8 @@ golang.org/x/text v0.8.0/go.mod h1:e1OnstbJyHTd6l/uOt8jFFHp6TRDWZR/bV3emEE/zU8=
 golang.org/x/time v0.0.0-20181108054448-85acf8d2951c/go.mod h1:tRJNPiyCQ0inRvYxbN9jk5I+vvW/OXSQhTDSoE431IQ=
 golang.org/x/time v0.0.0-20190308202827-9d24e82272b4/go.mod h1:tRJNPiyCQ0inRvYxbN9jk5I+vvW/OXSQhTDSoE431IQ=
 golang.org/x/time v0.0.0-20191024005414-555d28b269f0/go.mod h1:tRJNPiyCQ0inRvYxbN9jk5I+vvW/OXSQhTDSoE431IQ=
+golang.org/x/time v0.0.0-20210220033141-f8bda1e9f3ba h1:O8mE0/t419eoIwhTFpKVkHiTs/Igowgfkj25AcZrtiE=
+golang.org/x/time v0.0.0-20210220033141-f8bda1e9f3ba/go.mod h1:tRJNPiyCQ0inRvYxbN9jk5I+vvW/OXSQhTDSoE431IQ=
 golang.org/x/tools v0.0.0-20180917221912-90fa682c2a6e/go.mod h1:n7NCudcB/nEzxVGmLbDWY5pfWTLqBcC2KZ6jyYvM4mQ=
 golang.org/x/tools v0.0.0-20190114222345-bf090417da8b/go.mod h1:n7NCudcB/nEzxVGmLbDWY5pfWTLqBcC2KZ6jyYvM4mQ=
 golang.org/x/tools v0.0.0-20190226205152-f727befe758c/go.mod h1:9Yl7xja0Znq3iFh3HoIrodX9oNMXvdceNzlUR8zjMvY=
@@ -899,6 +959,7 @@ google.golang.org/genproto v0.0.0-20200228133532-8c2c7df3a383/go.mod h1:55QSHmfG
 google.golang.org/genproto v0.0.0-20200305110556-506484158171/go.mod h1:55QSHmfGQM9UVYDPBsyGGes0y52j32PQ3BqQfXhyH3c=
 google.golang.org/genproto v0.0.0-20200312145019-da6875a35672/go.mod h1:55QSHmfGQM9UVYDPBsyGGes0y52j32PQ3BqQfXhyH3c=
 google.golang.org/genproto v0.0.0-20200331122359-1ee6d9798940/go.mod h1:55QSHmfGQM9UVYDPBsyGGes0y52j32PQ3BqQfXhyH3c=
+google.golang.org/genproto v0.0.0-20200423170343-7949de9c1215/go.mod h1:55QSHmfGQM9UVYDPBsyGGes0y52j32PQ3BqQfXhyH3c=
 google.golang.org/genproto v0.0.0-20200430143042-b979b6f78d84/go.mod h1:55QSHmfGQM9UVYDPBsyGGes0y52j32PQ3BqQfXhyH3c=
 google.golang.org/genproto v0.0.0-20200511104702-f5ebc3bea380/go.mod h1:55QSHmfGQM9UVYDPBsyGGes0y52j32PQ3BqQfXhyH3c=
 google.golang.org/genproto v0.0.0-20200513103714-09dca8ec2884/go.mod h1:55QSHmfGQM9UVYDPBsyGGes0y52j32PQ3BqQfXhyH3c=
@@ -974,6 +1035,7 @@ google.golang.org/grpc v1.39.0/go.mod h1:PImNr+rS9TWYb2O4/emRugxiyHZ5JyHW5F+RPnD
 google.golang.org/grpc v1.39.1/go.mod h1:PImNr+rS9TWYb2O4/emRugxiyHZ5JyHW5F+RPnDzfrE=
 google.golang.org/grpc v1.40.0/go.mod h1:ogyxbiOoUXAkP+4+xa6PZSE9DZgIHtSpzjDTB9KAK34=
 google.golang.org/grpc v1.40.1/go.mod h1:ogyxbiOoUXAkP+4+xa6PZSE9DZgIHtSpzjDTB9KAK34=
+google.golang.org/grpc v1.41.0/go.mod h1:U3l9uK9J0sini8mHphKoXyaqDA/8VyGnDee1zzIUK6k=
 google.golang.org/grpc v1.44.0 h1:weqSxi/TMs1SqFRMHCtBgXRs8k3X39QIDEZ0pRcttUg=
 google.golang.org/grpc v1.44.0/go.mod h1:k+4IHHFw41K8+bbowsex27ge2rCb65oeWqe4jJ590SU=
 google.golang.org/grpc/cmd/protoc-gen-go-grpc v1.1.0/go.mod h1:6Kw0yEErY5E/yWrBtf03jp27GLLJujG4z/JK95pnjjw=
@@ -1006,6 +1068,8 @@ gopkg.in/go-playground/validator.v9 v9.20.2 h1:6AVDyt8bk0FDiSYSeWivUfzqEjHyVSCMR
 gopkg.in/go-playground/validator.v9 v9.20.2/go.mod h1:+c9/zcJMFNgbLvly1L1V+PpxWdVbfP1avr/N00E2vyQ=
 gopkg.in/ini.v1 v1.42.0 h1:7N3gPTt50s8GuLortA00n8AqRTk75qOP98+mTPpgzRk=
 gopkg.in/ini.v1 v1.42.0/go.mod h1:pNLf8WUiyNEtQjuu5G5vTm06TEv9tsIgeAvK8hOrP4k=
+gopkg.in/natefinch/lumberjack.v2 v2.0.0 h1:1Lc07Kr7qY4U2YPouBjpCLxpiyxIVoxqXgkXLknAOE8=
+gopkg.in/natefinch/lumberjack.v2 v2.0.0/go.mod h1:l0ndWWf7gzL7RNwBG7wST/UCcT4T24xpD6X8LsfU/+k=
 gopkg.in/tomb.v1 v1.0.0-20141024135613-dd632973f1e7 h1:uRGJdciOHaEIrze2W8Q3AKkepLTh2hOroT7a+7czfdQ=
 gopkg.in/tomb.v1 v1.0.0-20141024135613-dd632973f1e7/go.mod h1:dt/ZhP58zS4L8KSrWDmTeBkI65Dw0HsyUHuEVlX15mw=
 gopkg.in/yaml.v2 v2.2.1/go.mod h1:hI93XBmqTisBFMUTm0b8Fm+jr3Dg1NNxqwp+5A1VGuI=
@@ -1032,4 +1096,5 @@ howett.net/plist v0.0.0-20181124034731-591f970eefbb/go.mod h1:vMygbs4qMhSZSc4lCU
 rsc.io/binaryregexp v0.2.0/go.mod h1:qTv7/COck+e2FymRvadv62gMdZztPaShugOCi3I+8D8=
 rsc.io/quote/v3 v3.1.0/go.mod h1:yEA65RcK8LyAZtP9Kv3t0HmxON59tX3rD+tICJqUlj0=
 rsc.io/sampler v1.3.0/go.mod h1:T1hPZKmBbMNahiBKFy5HrXp6adAjACjK9JXDnKaTXpA=
+sigs.k8s.io/yaml v1.2.0 h1:kr/MCeFWJWTwyaHoR9c8EjH9OumOmoF9YGiZd7lFm/Q=
 sigs.k8s.io/yaml v1.2.0/go.mod h1:yfXDCHCao9+ENCvLSE62v9VSji2MKu5jeNfTrofGhJc=
diff --git a/pkg/errors/errors.go b/pkg/errors/errors.go
index 87af8ea7..6b502dc1 100644
--- a/pkg/errors/errors.go
+++ b/pkg/errors/errors.go
@@ -47,6 +47,8 @@ func (e Error) Error() string {
 	return e.Err.Error()
 }
 
+func (e Error) Unwrap() error { return e.Err }
+
 // Is is a shorthand for checking an error against a kind.
 func Is(err error, kind int) bool {
 	if err == nil {
diff --git a/pkg/stash/with_etcd.go b/pkg/stash/with_etcd.go
index 0d89424b..03c56fe7 100644
--- a/pkg/stash/with_etcd.go
+++ b/pkg/stash/with_etcd.go
@@ -38,33 +38,31 @@ func (s *etcd) Stash(ctx context.Context, mod, ver string) (newVer string, err e
 	const op errors.Op = "etcd.Stash"
 	ctx, span := observ.StartSpan(ctx, op.String())
 	defer span.End()
-	sesh, err := concurrency.NewSession(s.client)
+
+	sess, err := concurrency.NewSession(s.client)
 	if err != nil {
-		return ver, errors.E(op, err)
+		return "", errors.E(op, err)
 	}
-	mv := config.FmtModVer(mod, ver)
-	mu := concurrency.NewMutex(sesh, mv)
-	err = mu.Lock(ctx)
-	if err != nil {
-		return ver, errors.E(op, err)
+	defer sess.Close()
+
+	m := concurrency.NewMutex(sess, config.FmtModVer(mod, ver))
+	if err := m.Lock(ctx); err != nil {
+		return "", errors.E(op, err)
 	}
-	defer func() {
-		const op errors.Op = "etcd.Unlock"
-		lockErr := mu.Unlock(ctx)
-		if err == nil && lockErr != nil {
-			err = errors.E(op, lockErr)
-		}
-	}()
+	defer m.Unlock(ctx)
+
 	ok, err := s.checker.Exists(ctx, mod, ver)
 	if err != nil {
-		return ver, errors.E(op, err)
+		return "", errors.E(op, err)
 	}
+
 	if ok {
 		return ver, nil
 	}
+
 	newVer, err = s.stasher.Stash(ctx, mod, ver)
 	if err != nil {
-		return ver, errors.E(op, err)
+		return "", errors.E(op, err)
 	}
 	return newVer, nil
 }


Test patch:
diff --git a/pkg/stash/with_etcd_test.go b/pkg/stash/with_etcd_test.go
index 22768cfb..6be11f4a 100644
--- a/pkg/stash/with_etcd_test.go
+++ b/pkg/stash/with_etcd_test.go
@@ -2,82 +2,218 @@ package stash
 
 import (
 	"context"
-	"fmt"
-	"os"
-	"strings"
-	"sync"
+	"net/url"
 	"testing"
 	"time"
 
-	"github.com/gomods/athens/pkg/storage"
-	"github.com/gomods/athens/pkg/storage/mem"
-	"golang.org/x/sync/errgroup"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	"go.etcd.io/etcd/api/v3/etcdserverpb"
+	etcdembed "go.etcd.io/etcd/server/v3/embed"
 )
 
-// TestEtcdSingleFlight will ensure that 5 concurrent requests will all get the first request's
-// response. We can ensure that because only the first response does not return an error
-// and therefore all 5 responses should have no error.
-func TestEtcdSingleFlight(t *testing.T) {
-	endpointsStr := os.Getenv("ETCD_TEST_ENDPOINTS")
-	if len(endpointsStr) == 0 {
-		t.SkipNow()
-	}
-	strg, err := mem.NewStorage()
-	if err != nil {
-		t.Fatal(err)
-	}
-	ms := &mockEtcdStasher{strg: strg}
-	endpoints := strings.Split(endpointsStr, ",")
-	wrapper, err := WithEtcd(endpoints, storage.WithChecker(strg))
+type testContextKey struct{}
+
+type testError string
+
+func (e testError) Error() string { return string(e) }
+
+type mockChecker struct {
+	t                       *testing.T
+	e                       *etcdembed.Etcd
+	wantModule, wantVersion string
+
+	exists bool
+	err    error
+}
+
+func (c *mockChecker) Exists(ctx context.Context, module, version string) (bool, error) {
+	assert.NotNil(c.t, ctx.Value(testContextKey{}))
+	assert.Equal(c.t, c.wantModule, module)
+	assert.Equal(c.t, c.wantVersion, version)
+
+	res, err := c.e.Server.LeaseLeases(ctx, &etcdserverpb.LeaseLeasesRequest{})
+	require.NoError(c.t, err)
+
+	assert.Len(c.t, res.Leases, 1)
+
+	return c.exists, c.err
+}
+
+type mockStasher struct {
+	t                       *testing.T
+	wantModule, wantVersion string
+
+	newVersion string
+	err        error
+}
+
+func (s *mockStasher) Stash(ctx context.Context, module, version string) (string, error) {
+	assert.NotNil(s.t, ctx.Value(testContextKey{}))
+	assert.Equal(s.t, s.wantModule, module)
+	assert.Equal(s.t, s.wantVersion, version)
+	return s.newVersion, s.err
+}
+
+func startEtcdServer(t *testing.T) (endpoint string, e *etcdembed.Etcd) {
+	c := etcdembed.NewConfig()
+	c.Dir = t.TempDir()
+	c.ListenPeerUrls = []url.URL{{Host: "localhost:0"}}
+	c.ListenClientUrls = []url.URL{{Host: "localhost:0"}}
+
+	e, err := etcdembed.StartEtcd(c)
 	if err != nil {
 		t.Fatal(err)
 	}
-	s := wrapper(ms)
-
-	var eg errgroup.Group
-	for i := 0; i < 5; i++ {
-		eg.Go(func() error {
-			ctx, cancel := context.WithTimeout(context.Background(), time.Second*10)
-			defer cancel()
-			_, err := s.Stash(ctx, "mod", "ver")
-			return err
-		})
+	t.Cleanup(func() { e.Close() })
+
+	deadline, ok := t.Deadline()
+	if !ok {
+		deadline = time.Now().Add(5 * time.Second)
 	}
 
-	err = eg.Wait()
-	if err != nil {
-		t.Fatal(err)
+	select {
+	case <-e.Server.ReadyNotify():
+	case <-time.After(time.Until(deadline)):
+		t.Fatal("etcd server startup duration exceeded deadline")
 	}
+	return e.Clients[0].Addr().String(), e
 }
 
-// mockEtcdStasher is like mockStasher
-// but leverages in memory storage
-// so that etcd can determine
-// whether to call the underlying stasher or not.
-type mockEtcdStasher struct {
-	strg storage.Backend
-	mu   sync.Mutex
-	num  int
+func TestWithEtcd(t *testing.T) {
+	endpoint, _ := startEtcdServer(t)
+
+	var someChecker mockChecker
+	w, err := WithEtcd([]string{endpoint}, &someChecker)
+	require.NoError(t, err)
+
+	var someStasher mockStasher
+	etcdSingleflight, ok := w(&someStasher).(*etcd)
+	require.True(t, ok)
+
+	assert.Equal(t, etcdSingleflight.checker, &someChecker)
+	assert.Equal(t, etcdSingleflight.stasher, &someStasher)
 }
 
-func (ms *mockEtcdStasher) Stash(ctx context.Context, mod, ver string) (string, error) {
-	time.Sleep(time.Millisecond * 100) // allow for second requests to come in.
-	ms.mu.Lock()
-	defer ms.mu.Unlock()
-	if ms.num == 0 {
-		err := ms.strg.Save(
-			ctx,
-			mod,
-			ver,
-			[]byte("mod file"),
-			strings.NewReader("zip file"),
-			[]byte("info file"),
+func TestEtcdStash(t *testing.T) {
+	t.Run("module exists", func(t *testing.T) {
+		endpoint, e := startEtcdServer(t)
+
+		const (
+			someModule  = "some module"
+			someVersion = "some version"
 		)
-		if err != nil {
-			return "", err
-		}
-		ms.num++
-		return "", nil
-	}
-	return "", fmt.Errorf("second time error")
+
+		ctx := context.WithValue(context.Background(), testContextKey{}, struct{}{})
+
+		w, err := WithEtcd([]string{endpoint}, &mockChecker{
+			t:           t,
+			e:           e,
+			wantModule:  someModule,
+			wantVersion: someVersion,
+			exists:      true,
+		})
+		require.NoError(t, err)
+
+		newVersion, err := w(&mockStasher{
+			t:           t,
+			wantModule:  someModule,
+			wantVersion: someVersion,
+		}).Stash(ctx, someModule, someVersion)
+		require.NoError(t, err)
+
+		assert.Equal(t, someVersion, newVersion)
+
+		res, err := e.Server.LeaseLeases(ctx, &etcdserverpb.LeaseLeasesRequest{})
+		require.NoError(t, err)
+
+		assert.Empty(t, res.Leases)
+	})
+
+	t.Run("module does not exist", func(t *testing.T) {
+		endpoint, e := startEtcdServer(t)
+
+		const (
+			someModule  = "some module"
+			someVersion = "some version"
+
+			someNewVersion = "some new version"
+		)
+
+		ctx := context.WithValue(context.Background(), testContextKey{}, struct{}{})
+
+		w, err := WithEtcd([]string{endpoint}, &mockChecker{
+			t:           t,
+			e:           e,
+			wantModule:  someModule,
+			wantVersion: someVersion,
+		})
+		require.NoError(t, err)
+
+		newVersion, err := w(&mockStasher{
+			t:           t,
+			wantModule:  someModule,
+			wantVersion: someVersion,
+			newVersion:  someNewVersion,
+		}).Stash(ctx, someModule, someVersion)
+		require.NoError(t, err)
+
+		assert.Equal(t, someNewVersion, newVersion)
+	})
+
+	t.Run("checker error", func(t *testing.T) {
+		endpoint, e := startEtcdServer(t)
+
+		const (
+			someModule  = "some module"
+			someVersion = "some version"
+
+			someError testError = "some error"
+		)
+
+		ctx := context.WithValue(context.Background(), testContextKey{}, struct{}{})
+
+		w, err := WithEtcd([]string{endpoint}, &mockChecker{
+			t:           t,
+			e:           e,
+			wantModule:  someModule,
+			wantVersion: someVersion,
+			err:         someError,
+		})
+		require.NoError(t, err)
+
+		newVersion, err := w(&mockStasher{}).Stash(ctx, someModule, someVersion)
+		assert.ErrorIs(t, err, someError)
+		assert.Empty(t, newVersion)
+	})
+
+	t.Run("stasher error", func(t *testing.T) {
+		endpoint, e := startEtcdServer(t)
+
+		const (
+			someModule  = "some module"
+			someVersion = "some version"
+
+			someError testError = "some error"
+		)
+
+		ctx := context.WithValue(context.Background(), testContextKey{}, struct{}{})
+
+		w, err := WithEtcd([]string{endpoint}, &mockChecker{
+			t:           t,
+			e:           e,
+			wantModule:  someModule,
+			wantVersion: someVersion,
+		})
+		require.NoError(t, err)
+
+		newVersion, err := w(&mockStasher{
+			t:           t,
+			wantModule:  someModule,
+			wantVersion: someVersion,
+			err:         someError,
+		}).Stash(ctx, someModule, someVersion)
+		assert.ErrorIs(t, err, someError)
+		assert.Empty(t, newVersion)
+	})
 }