Log metadata diffs on upserts

Before performing an upsert, log the differences between the existing
metadata and the new metadata. This will help us understand what is
happening when we see unexpected changes in the metadata.

go.mod

@@ -95,7 +95,7 @@ require (
 	github.com/modern-go/concurrent v0.0.0-20180306012644-bacd9c7ef1dd // indirect
 	github.com/modern-go/reflect2 v1.0.2 // indirect
 	github.com/pelletier/go-toml/v2 v2.1.0 // indirect
-	github.com/pmezard/go-difflib v1.0.1-0.20181226105442-5d4384ee4fb2 // indirect
+	github.com/pmezard/go-difflib v1.0.1-0.20181226105442-5d4384ee4fb2
 	github.com/pressly/goose/v3 v3.15.0 // indirect
 	github.com/prometheus/client_model v0.5.0 // indirect
 	github.com/prometheus/common v0.45.0 // indirect

go.sum

@@ -120,8 +120,6 @@ github.com/cncf/xds/go v0.0.0-20211001041855-01bcc9b48dfe/go.mod h1:eXthEFrGJvWH
 github.com/cncf/xds/go v0.0.0-20211011173535-cb28da3451f1/go.mod h1:eXthEFrGJvWHgFFCl3hGmgk+/aYT6PnTQLykKQRLhEs=
 github.com/cockroachdb/apd v1.1.0 h1:3LFP3629v+1aKXU5Q37mxmRxX/pIu1nijXydLShEq5I=
 github.com/cockroachdb/apd v1.1.0/go.mod h1:8Sl8LxpKi29FqWXR16WEFZRNSz3SoPzUzeMeY4+DwBQ=
-github.com/cockroachdb/cockroach-go/v2 v2.3.5 h1:Khtm8K6fTTz/ZCWPzU9Ne3aOW9VyAnj4qIPCJgKtwK0=
-github.com/cockroachdb/cockroach-go/v2 v2.3.5/go.mod h1:1wNJ45eSXW9AnOc3skntW9ZUZz6gxrQK3cOj3rK+BC8=
 github.com/cockroachdb/cockroach-go/v2 v2.3.6 h1:Wlv9TzkrG9V7i6u8dEtmXPrBzvfFp+CgJNs696rAajM=
 github.com/cockroachdb/cockroach-go/v2 v2.3.6/go.mod h1:1wNJ45eSXW9AnOc3skntW9ZUZz6gxrQK3cOj3rK+BC8=
 github.com/coreos/go-oidc/v3 v3.9.0 h1:0J/ogVOd4y8P0f0xUh8l9t07xRP/d8tccvjHl2dcsSo=
@@ -203,8 +201,6 @@ github.com/go-playground/universal-translator v0.17.0/go.mod h1:UkSxE5sNxxRwHyU+
 github.com/go-playground/universal-translator v0.18.1 h1:Bcnm0ZwsGyWbCzImXv+pAJnYK9S473LQFuzCbDbfSFY=
 github.com/go-playground/universal-translator v0.18.1/go.mod h1:xekY+UJKNuX9WP91TpwSH2VMlDf28Uj24BCp08ZFTUY=
 github.com/go-playground/validator/v10 v10.2.0/go.mod h1:uOYAAleCW8F/7oMFd6aG0GOhaH6EGOAJShg8Id5JGkI=
-github.com/go-playground/validator/v10 v10.16.0 h1:x+plE831WK4vaKHO/jpgUGsvLKIqRRkz6M78GuJAfGE=
-github.com/go-playground/validator/v10 v10.16.0/go.mod h1:9iXMNT7sEkjXb0I+enO7QXmzG6QCsPWY4zveKFVRSyU=
 github.com/go-playground/validator/v10 v10.17.0 h1:SmVVlfAOtlZncTxRuinDPomC2DkXJ4E5T9gDA0AIH74=
 github.com/go-playground/validator/v10 v10.17.0/go.mod h1:9iXMNT7sEkjXb0I+enO7QXmzG6QCsPWY4zveKFVRSyU=
 github.com/go-sql-driver/mysql v1.6.0/go.mod h1:DCzpHaOWr8IXmIStZouvnhqoel9Qv2LBy8hT2VhHyBg=
@@ -306,8 +302,6 @@ github.com/google/renameio v0.1.0/go.mod h1:KWCgfxg9yswjAJkECMjeO8J8rahYeXnNhOm4
 github.com/google/uuid v1.1.1/go.mod h1:TIyPZe4MgqvfeYDBFedMoGGpEw/LqOeaOT+nhxU+yHo=
 github.com/google/uuid v1.1.2/go.mod h1:TIyPZe4MgqvfeYDBFedMoGGpEw/LqOeaOT+nhxU+yHo=
 github.com/google/uuid v1.3.0/go.mod h1:TIyPZe4MgqvfeYDBFedMoGGpEw/LqOeaOT+nhxU+yHo=
-github.com/google/uuid v1.5.0 h1:1p67kYwdtXjb0gL0BPiP1Av9wiZPo5A8z2cWkTZ+eyU=
-github.com/google/uuid v1.5.0/go.mod h1:TIyPZe4MgqvfeYDBFedMoGGpEw/LqOeaOT+nhxU+yHo=
 github.com/google/uuid v1.6.0 h1:NIvaJDMOsjHA8n1jAhLSgzrAzy1Hgr+hNrb57e+94F0=
 github.com/google/uuid v1.6.0/go.mod h1:TIyPZe4MgqvfeYDBFedMoGGpEw/LqOeaOT+nhxU+yHo=
 github.com/googleapis/gax-go/v2 v2.0.4/go.mod h1:0Wqv26UfaUD9n4G6kQubkQ+KchISgw+vpHVxEJEs9eg=
@@ -648,12 +642,9 @@ github.com/volatiletech/null/v8 v8.1.2 h1:kiTiX1PpwvuugKwfvUNX/SU/5A2KGZMXfGD0DU
 github.com/volatiletech/null/v8 v8.1.2/go.mod h1:98DbwNoKEpRrYtGjWFctievIfm4n4MxG0A6EBUcoS5g=
 github.com/volatiletech/randomize v0.0.1 h1:eE5yajattWqTB2/eN8df4dw+8jwAzBtbdo5sbWC4nMk=
 github.com/volatiletech/randomize v0.0.1/go.mod h1:GN3U0QYqfZ9FOJ67bzax1cqZ5q2xuj2mXrXBjWaRTlY=
-github.com/volatiletech/sqlboiler/v4 v4.15.0 h1:+twm3mA34SaUF6wB9U6QkXxkK8AKkV5EfgMSvcKWeY4=
-github.com/volatiletech/sqlboiler/v4 v4.15.0/go.mod h1:s643wqYyCQ7Ak2hMVxH7kTS0+lFPNlj+gHKUIukJ0YA=
 github.com/volatiletech/sqlboiler/v4 v4.16.1 h1:utSd0n+zoasYAGOwbeGzzLb3p9vdItRyYR6zm20SVP0=
 github.com/volatiletech/sqlboiler/v4 v4.16.1/go.mod h1:B14BPBGTrJ2X6l7lwnvV/iXgYR48+ozGSlzHI3frl6U=
 github.com/volatiletech/strmangle v0.0.1/go.mod h1:F6RA6IkB5vq0yTG4GQ0UsbbRcl3ni9P76i+JrTBKFFg=
-github.com/volatiletech/strmangle v0.0.5/go.mod h1:ycDvbDkjDvhC0NUU8w3fWwl5JEMTV56vTKXzR3GeR+0=
 github.com/volatiletech/strmangle v0.0.6 h1:AdOYE3B2ygRDq4rXDij/MMwq6KVK/pWAYxpC7CLrkKQ=
 github.com/volatiletech/strmangle v0.0.6/go.mod h1:ycDvbDkjDvhC0NUU8w3fWwl5JEMTV56vTKXzR3GeR+0=
 github.com/yuin/goldmark v1.1.25/go.mod h1:3hX8gzYuyVAZsxl0MRgGTJEmQBFcNTphYh9decYSb74=
@@ -680,16 +671,10 @@ go.opencensus.io v0.22.3/go.mod h1:yxeiOL68Rb0Xd1ddK5vPZ/oVn4vY4Ynel7k9FzqtOIw=
 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/go.mod h1:XItmlyltB5F7CS4xOC1DcqMoFqwtC6OG2xF7mCv7P7E=
-go.opentelemetry.io/contrib/instrumentation/github.com/gin-gonic/gin/otelgin v0.45.0 h1:0KYeVr81ogcVRLXVcXFuPQMNZngplnP8MqrE8CqvHeg=
-go.opentelemetry.io/contrib/instrumentation/github.com/gin-gonic/gin/otelgin v0.45.0/go.mod h1:ro3eEFOynMu0p59YVUFFbkOeaPREbqc5yDR2HnGpFc0=
-go.opentelemetry.io/contrib/instrumentation/github.com/gin-gonic/gin/otelgin v0.46.1 h1:mMv2jG58h6ZI5t5S9QCVGdzCmAsTakMa3oxVgpSD44g=
-go.opentelemetry.io/contrib/instrumentation/github.com/gin-gonic/gin/otelgin v0.46.1/go.mod h1:oqRuNKG0upTaDPbLVCG8AD0G2ETrfDtmh7jViy7ox6M=
 go.opentelemetry.io/contrib/instrumentation/github.com/gin-gonic/gin/otelgin v0.48.0 h1:9fRyGkm/rbLuNNJsk9YY2c7Tpjf9tRjm1BAa48L3ypU=
 go.opentelemetry.io/contrib/instrumentation/github.com/gin-gonic/gin/otelgin v0.48.0/go.mod h1:7eRxLMX2ua+Pwtw1lkj8L0i0aykVQ/CafXhARYY056k=
-go.opentelemetry.io/contrib/propagators/b3 v1.20.0 h1:Yty9Vs4F3D6/liF1o6FNt0PvN85h/BJJ6DQKJ3nrcM0=
-go.opentelemetry.io/contrib/propagators/b3 v1.20.0/go.mod h1:On4VgbkqYL18kbJlWsa18+cMNe6rYpBnPi1ARI/BrsU=
-go.opentelemetry.io/otel v1.21.0 h1:hzLeKBZEL7Okw2mGzZ0cc4k/A7Fta0uoPgaJCr8fsFc=
-go.opentelemetry.io/otel v1.21.0/go.mod h1:QZzNPQPm1zLX4gZK4cMi+71eaorMSGT3A4znnUvNNEo=
+go.opentelemetry.io/contrib/propagators/b3 v1.23.0 h1:aaIGWc5JdfRGpCafLRxMJbD65MfTa206AwSKkvGS0Hg=
+go.opentelemetry.io/contrib/propagators/b3 v1.23.0/go.mod h1:Gyz7V7XghvwTq+mIhLFlTgcc03UDroOg8vezs4NLhwU=
 go.opentelemetry.io/otel v1.23.1 h1:Za4UzOqJYS+MUczKI320AtqZHZb7EqxO00jAHE0jmQY=
 go.opentelemetry.io/otel v1.23.1/go.mod h1:Td0134eafDLcTS4y+zQ26GE8u3dEuRBiBCTUIRHaikA=
 go.opentelemetry.io/otel/exporters/jaeger v1.17.0 h1:D7UpUy2Xc2wsi1Ras6V40q806WM07rqoCWzXu7Sqy+4=
@@ -702,16 +687,12 @@ go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracehttp v1.21.0 h1:digkE
 go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracehttp v1.21.0/go.mod h1:/OpE/y70qVkndM0TrxT4KBoN3RsFZP0QaofcfYrj76I=
 go.opentelemetry.io/otel/exporters/stdout/stdouttrace v1.21.0 h1:VhlEQAPp9R1ktYfrPk5SOryw1e9LDDTZCbIPFrho0ec=
 go.opentelemetry.io/otel/exporters/stdout/stdouttrace v1.21.0/go.mod h1:kB3ufRbfU+CQ4MlUcqtW8Z7YEOBeK2DJ6CmR5rYYF3E=
-go.opentelemetry.io/otel/metric v1.21.0 h1:tlYWfeo+Bocx5kLEloTjbcDwBuELRrIFxwdQ36PlJu4=
-go.opentelemetry.io/otel/metric v1.21.0/go.mod h1:o1p3CA8nNHW8j5yuQLdc1eeqEaPfzug24uvsyIEJRWM=
 go.opentelemetry.io/otel/metric v1.23.1 h1:PQJmqJ9u2QaJLBOELl1cxIdPcpbwzbkjfEyelTl2rlo=
 go.opentelemetry.io/otel/metric v1.23.1/go.mod h1:mpG2QPlAfnK8yNhNJAxDZruU9Y1/HubbC+KyH8FaCWI=
 go.opentelemetry.io/otel/sdk v1.21.0 h1:FTt8qirL1EysG6sTQRZ5TokkU8d0ugCj8htOgThZXQ8=
 go.opentelemetry.io/otel/sdk v1.21.0/go.mod h1:Nna6Yv7PWTdgJHVRD9hIYywQBRx7pbox6nwBnZIxl/E=
 go.opentelemetry.io/otel/sdk/metric v0.39.0 h1:Kun8i1eYf48kHH83RucG93ffz0zGV1sh46FAScOTuDI=
 go.opentelemetry.io/otel/sdk/metric v0.39.0/go.mod h1:piDIRgjcK7u0HCL5pCA4e74qpK/jk3NiUoAHATVAmiI=
-go.opentelemetry.io/otel/trace v1.21.0 h1:WD9i5gzvoUPuXIXH24ZNBudiarZDKuekPqi/E8fpfLc=
-go.opentelemetry.io/otel/trace v1.21.0/go.mod h1:LGbsEB0f9LGjN+OZaQQ26sohbOmiMR+BaslueVtS/qQ=
 go.opentelemetry.io/otel/trace v1.23.1 h1:4LrmmEd8AU2rFvU1zegmvqW7+kWarxtNOPyeL6HmYY8=
 go.opentelemetry.io/otel/trace v1.23.1/go.mod h1:4IpnpJFwr1mo/6HL8XIPJaE9y0+u1KcVmuW7dwFSVrI=
 go.opentelemetry.io/proto/otlp v0.7.0/go.mod h1:PqfVotwruBrMGOCsRd/89rSnXhoiJIqeYNgFYFoEGnI=
@@ -764,8 +745,6 @@ golang.org/x/crypto v0.0.0-20220411220226-7b82a4e95df4/go.mod h1:IxCIyHEi3zRg3s0
 golang.org/x/crypto v0.0.0-20220511200225-c6db032c6c88/go.mod h1:IxCIyHEi3zRg3s0A5j5BB6A9Jmi73HwBIUl50j+osU4=
 golang.org/x/crypto v0.0.0-20220826181053-bd7e27e6170d/go.mod h1:IxCIyHEi3zRg3s0A5j5BB6A9Jmi73HwBIUl50j+osU4=
 golang.org/x/crypto v0.6.0/go.mod h1:OFC/31mSvZgRz0V1QTNCzfAI1aIRzbiufJtkMIlEp58=
-golang.org/x/crypto v0.17.0 h1:r8bRNjWL3GshPW3gkd+RpvzWrZAwPS49OmTGZ/uhM4k=
-golang.org/x/crypto v0.17.0/go.mod h1:gCAAfMLgwOJRpTjQ2zCCt2OcSfYMTeZVSRtQlPC7Nq4=
 golang.org/x/crypto v0.19.0 h1:ENy+Az/9Y1vSrlrvBSyna3PITt4tiZLf7sgCjZBX7Wo=
 golang.org/x/crypto v0.19.0/go.mod h1:Iy9bg/ha4yyC70EfRS8jz+B6ybOBKMaSxLj6P6oBDfU=
 golang.org/x/exp v0.0.0-20190121172915-509febef88a4/go.mod h1:CJ0aWSM057203Lf6IL+f9T1iT9GByDxfZKAQTCR3kQA=
@@ -859,8 +838,6 @@ golang.org/x/net v0.0.0-20220425223048-2871e0cb64e4/go.mod h1:CfG3xpIq0wQ8r1q4Su
 golang.org/x/net v0.0.0-20220520000938-2e3eb7b945c2/go.mod h1:CfG3xpIq0wQ8r1q4Su4UZFWDARRcnwPjda9FqA0JpMk=
 golang.org/x/net v0.0.0-20220722155237-a158d28d115b/go.mod h1:XRhObCWvk6IyKnWLug+ECip1KBveYUHfp+8e9klMJ9c=
 golang.org/x/net v0.6.0/go.mod h1:2Tu9+aMcznHK/AK1HMvgo6xiTLG5rD5rZLDS+rp2Bjs=
-golang.org/x/net v0.19.0 h1:zTwKpTd2XuCqf8huc7Fo2iSy+4RHPd10s4KzeTnVr1c=
-golang.org/x/net v0.19.0/go.mod h1:CfAk/cbD4CthTvqiEl8NpboMuiuOYsAr/7NOjZJtv1U=
 golang.org/x/net v0.21.0 h1:AQyQV4dYCvJ7vGmJyKki9+PBdyvhkSd8EIx/qb0AYv4=
 golang.org/x/net v0.21.0/go.mod h1:bIjVDfnllIU7BJ2DNgfnXvpSvtn8VRwhlsaeUTyUS44=
 golang.org/x/oauth2 v0.0.0-20180821212333-d2e6202438be/go.mod h1:N/0e6XlmueqKjAGxoOufVs8QHGRruUQn6yWY3a++T0U=
@@ -883,8 +860,6 @@ golang.org/x/oauth2 v0.0.0-20211104180415-d3ed0bb246c8/go.mod h1:KelEdhl1UZF7XfJ
 golang.org/x/oauth2 v0.0.0-20220223155221-ee480838109b/go.mod h1:DAh4E804XQdzx2j+YRIaUnCqCV2RuMz24cGBJ5QYIrc=
 golang.org/x/oauth2 v0.0.0-20220309155454-6242fa91716a/go.mod h1:DAh4E804XQdzx2j+YRIaUnCqCV2RuMz24cGBJ5QYIrc=
 golang.org/x/oauth2 v0.0.0-20220411215720-9780585627b5/go.mod h1:DAh4E804XQdzx2j+YRIaUnCqCV2RuMz24cGBJ5QYIrc=
-golang.org/x/oauth2 v0.15.0 h1:s8pnnxNVzjWyrvYdFUQq5llS1PX2zhPXmccZv99h7uQ=
-golang.org/x/oauth2 v0.15.0/go.mod h1:q48ptWNTY5XWf+JNten23lcvHpLJ0ZSxF5ttTHKVCAM=
 golang.org/x/oauth2 v0.17.0 h1:6m3ZPmLEFdVxKKWnKq4VqZ60gutO35zm+zrAHVmHyDQ=
 golang.org/x/oauth2 v0.17.0/go.mod h1:OzPDGQiuQMguemayvdylqddI7qcD9lnSDb+1FiwQ5HA=
 golang.org/x/sync v0.0.0-20180314180146-1d60e4601c6f/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
@@ -988,8 +963,6 @@ golang.org/x/sys v0.0.0-20220811171246-fbc7d0a398ab/go.mod h1:oPkhp1MJrh7nUepCBc
 golang.org/x/sys v0.0.0-20220825204002-c680a09ffe64/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.5.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.6.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
-golang.org/x/sys v0.15.0 h1:h48lPFYpsTvQJZF4EKyI4aLHaev3CxivZmv7yZig9pc=
-golang.org/x/sys v0.15.0/go.mod h1:/VUhepiaJMQUp4+oa/7Zr1D23ma6VTLIYjOOTFZPUcA=
 golang.org/x/sys v0.17.0 h1:25cE3gD+tdBA7lp7QfhuV+rJiE9YXTcS3VG1SqssI/Y=
 golang.org/x/sys v0.17.0/go.mod h1:/VUhepiaJMQUp4+oa/7Zr1D23ma6VTLIYjOOTFZPUcA=
 golang.org/x/term v0.0.0-20201117132131-f5c789dd3221/go.mod h1:Nr5EML6q2oocZ2LXRh80K7BxOlk5/8JxuGnuhpl+muw=
@@ -1266,8 +1239,6 @@ google.golang.org/protobuf v1.26.0-rc.1/go.mod h1:jlhhOSvTdKEhbULTjvd4ARK9grFBp0
 google.golang.org/protobuf v1.26.0/go.mod h1:9q0QmTI4eRPtz6boOQmLYwt+qCgq0jsYwAQnmE0givc=
 google.golang.org/protobuf v1.27.1/go.mod h1:9q0QmTI4eRPtz6boOQmLYwt+qCgq0jsYwAQnmE0givc=
 google.golang.org/protobuf v1.28.0/go.mod h1:HV8QOd/L58Z+nl8r43ehVNZIU/HEI6OcFqwMG9pJV4I=
-google.golang.org/protobuf v1.31.0 h1:g0LDEJHgrBl9N9r17Ru3sqWhkIx2NB67okBHPwC7hs8=
-google.golang.org/protobuf v1.31.0/go.mod h1:HV8QOd/L58Z+nl8r43ehVNZIU/HEI6OcFqwMG9pJV4I=
 google.golang.org/protobuf v1.32.0 h1:pPC6BG5ex8PDFnkbrGU3EixyhKcQ2aDuBS36lqK/C7I=
 google.golang.org/protobuf v1.32.0/go.mod h1:c6P6GXX6sHbq/GpV6MGZEdwhWPcYBgnhAHhKbcUYpos=
 gopkg.in/alecthomas/kingpin.v2 v2.2.6/go.mod h1:FMv+mEhP44yOT+4EoQTLFTRgOQ1FBLkstjWtayDeSgw=

pkg/api/v1/router_instance_metadata.go

@@ -5,12 +5,16 @@ import (
 	"database/sql"
 	"encoding/json"
 	"errors"
+	"fmt"
+	"log"
 	"math/rand"
 	"net/http"
+	"reflect"
 	"strconv"
 	"time"
 
 	"github.com/gin-gonic/gin"
+	"github.com/pmezard/go-difflib/difflib"
 	"github.com/spf13/viper"
 	"github.com/volatiletech/null/v8"
 	"github.com/volatiletech/sqlboiler/v4/types"
@@ -267,6 +271,9 @@ func (r *Router) instanceMetadataSet(c *gin.Context) {
 		Metadata: types.JSON(params.Metadata),
 	}
 
+	// Log the difference between the metadata we're about to upsert and the metadata we have in the database
+	instanceMetadataLogDiffs(r, c, newInstanceMetadata)
+
 	err := upserter.UpsertMetadata(c, r.DB, r.Logger, params.ID, params.getIPAddresses(), newInstanceMetadata)
 	if err != nil {
 		dbErrorResponse(r.Logger, c, err)
@@ -275,6 +282,69 @@ func (r *Router) instanceMetadataSet(c *gin.Context) {
 	c.Status(http.StatusOK)
 }
 
+// Log the difference between the metadata we're about to upsert and the metadata we have in the database
+func instanceMetadataLogDiffs(r *Router, c *gin.Context, newInstanceMetadata *models.InstanceMetadatum) {
+	instanceID := newInstanceMetadata.ID
+
+	existingMetadata, err := models.FindInstanceMetadatum(c.Request.Context(), r.DB, instanceID)
+	if err != nil && !errors.Is(err, sql.ErrNoRows) {
+		r.Logger.Sugar().Info("Upsert metadata diff for instance ", instanceID, ": this is the first metadata for this instance (sql.ErrNoRows)")
+		return
+	}
+
+	if existingMetadata == nil {
+		r.Logger.Sugar().Info("Upsert metadata diff for instance ", instanceID, ": this is the first metadata for this instance")
+		return
+	}
+
+	if existingMetadata != nil {
+		r.Logger.Sugar().Info("Upsert metadata diff for instance ", instanceID, ": ", diffJSON(r, instanceID, existingMetadata.Metadata, newInstanceMetadata.Metadata))
+	}
+}
+
+// diffJSON returns a string representation of the difference between two JSON objects
+func diffJSON(r *Router, instanceID string, existingJSON, newJSON types.JSON) string {
+	var existingMap, newMap map[string]interface{}
+
+	err := existingJSON.Unmarshal(&existingMap)
+	if err != nil {
+		return "Error unmarshalling existing JSON"
+	}
+
+	r.Logger.Sugar().Info("Existing metadata for instance ", instanceID, "has ", len(existingMap), " keys")
+
+	err = newJSON.Unmarshal(&newMap)
+	if err != nil {
+		return "Error unmarshalling new JSON"
+	}
+
+	r.Logger.Sugar().Info("New metadata for instance ", instanceID, "has ", len(newMap), " keys")
+
+	return diffMap(existingMap, newMap)
+}
+
+// diffMap returns a string representation of the difference between two maps
+func diffMap(existingMap, newMap map[string]interface{}) string {
+	var diff difflib.UnifiedDiff
+
+	if reflect.DeepEqual(existingMap, newMap) {
+		return "No difference"
+	}
+
+	// Generate a unified diff between the two maps
+	diff = difflib.UnifiedDiff{
+		A: difflib.SplitLines(fmt.Sprintf("%#v", existingMap)),
+		B: difflib.SplitLines(fmt.Sprintf("%#v", newMap)),
+	}
+
+	diffText, err := difflib.GetUnifiedDiffString(diff)
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	return diffText
+}
+
 func (r *Router) instanceUserdataSet(c *gin.Context) {
 	params := UpsertUserdataRequest{}