DRIVERS-2723: ensure atlas cluster names are unique (#351)

.evergreen/atlas/setup-atlas-cluster.sh

@@ -26,6 +26,7 @@ DRIVERS_ATLAS_LAMBDA_USER
 DRIVERS_ATLAS_LAMBDA_PASSWORD
 LAMBDA_STACK_NAME
 task_id
+execution
 )
 
 # Ensure that all variables required to run the test are set, otherwise throw

.evergreen/atlas/setup-variables.sh

@@ -20,7 +20,15 @@ ATLAS_API_VERSION="v1.0"
 ATLAS_BASE_URL="https://cloud.mongodb.com/api/atlas/$ATLAS_API_VERSION"
 
 # create a unique per CI task tag for the function.
-TASK_NAME=$(echo $task_id | base64 | head -c 8)
+# task_id has the structure $projectID_$variantName_$taskName_$commitHash_$createTime, which is unique per task per ci run per project.
+# task_id is NOT unique across restarts of the same task though, so we include execution to ensure that it is unique for every restart too.
+# 
+# the generated string is then transformed to satisfy Atlas cluster naming requirements
+# - the string cannot be > 64 characters long, so we hash the name to shorten it and maintain its uniqueness (hashes do have collisions but infrequently 
+#   enough that hashing suffices here)
+# - we convert it to hex encoding because cluster names must be alphanumeric (hyphens are allowed)
+transform="process.stdout.write(require('crypto').createHash('md5').update(process.argv[1]).digest().toString('hex'))"
+TASK_ID=$(node -e $transform "${task_id}-${execution}")
 
 # Add git commit to name of function and cluster.
-FUNCTION_NAME="${LAMBDA_STACK_NAME}-${TASK_NAME}-$(git rev-parse --short HEAD)"
+FUNCTION_NAME="${LAMBDA_STACK_NAME}-${TASK_ID}"

.evergreen/atlas/teardown-atlas-cluster.sh

@@ -19,6 +19,7 @@ DRIVERS_ATLAS_PRIVATE_API_KEY
 DRIVERS_ATLAS_GROUP_ID
 LAMBDA_STACK_NAME
 task_id
+execution
 )
 
 # Ensure that all variables required to run the test are set, otherwise throw