Detect when WEB_CONCURRENCY is way too high

profile/WEB_CONCURRENCY.sh

@@ -4,6 +4,9 @@ calculate_concurrency() {
   WEB_CONCURRENCY=${WEB_CONCURRENCY-$((MEMORY_AVAILABLE/WEB_MEMORY))}
   if (( WEB_CONCURRENCY < 1 )); then
     WEB_CONCURRENCY=1
+  elif (( WEB_CONCURRENCY > 100 )); then
+    # Ex: This will happen on Dokku on DO
+    WEB_CONCURRENCY=1
   fi
   echo $WEB_CONCURRENCY
 }
@@ -23,6 +26,22 @@ detect_memory() {
   fi
 }
 
+warn_bad_web_concurrency() {
+  local memory=${MEMORY_AVAILABLE-$(detect_memory 512)}
+
+  # No webserver will have 10000GB of RAM
+  if [ $memory -gt "10000000" ]; then
+    echo "Could not determine a reasonable value for WEB_CONCCURENCY.
+This is likely due to running the Heroku NodeJS buildpack on a non-Heroku
+platform.
+
+WEB_CONCURRENCY has been set to 1. Please review whether this value is
+appropriate for your application."
+  fi
+}
+
+warn_bad_web_concurrency
+
 export MEMORY_AVAILABLE=${MEMORY_AVAILABLE-$(detect_memory 512)}
 export WEB_MEMORY=${WEB_MEMORY-512}
 export WEB_CONCURRENCY=$(calculate_concurrency)

test/run

@@ -386,6 +386,15 @@ testConcurrencyCustomLimit() {
   assertCapturedSuccess
 }
 
+# When /sys/fs/cgroup/memory/memory.limit_in_bytes lies and gives a ridiculous value
+# This happens on Dokku for example
+testConcurrencyTooHigh() {
+  LOG_CONCURRENCY=true MEMORY_AVAILABLE=10000000000 capture $(pwd)/profile/WEB_CONCURRENCY.sh
+  assertCaptured "Could not determine a reasonable value for WEB_CONCCURENCY"
+  assertCaptured "Recommending WEB_CONCURRENCY=1"
+  assertCapturedSuccess
+}
+
 testInvalidNode() {
   compile "invalid-node"
   assertCaptured "Resolving node version 0.11.333"