fix: handle case where memory.limit_in_bytes is nonsensically large (#531)

* fix: handle case where memory.limit_in_bytes is nonsensically large

In certain CI environments, this value can be misreported, resulting in an invalid initial `MEMORY_AVAILABLE` value. In these cases, we default the max detected memory to 16GB, or slightly larger than a `performance-l` instance.

profile/WEB_CONCURRENCY.sh

 #!/usr/bin/env bash
 
 calculate_concurrency() {
-  WEB_CONCURRENCY=${WEB_CONCURRENCY-$((MEMORY_AVAILABLE/WEB_MEMORY))}
-  if (( WEB_CONCURRENCY < 1 )); then
-    WEB_CONCURRENCY=1
-  elif (( WEB_CONCURRENCY > 200 )); then
+  local available=$1
+  local web_memory=$2
+  local concurrency
+
+  concurrency=${WEB_CONCURRENCY-$(($available/$web_memory))}
+  if (( concurrency < 1 )); then
+    concurrency=1
+  elif (( concurrency > 200 )); then
     # Ex: This will happen on Dokku on DO
-    WEB_CONCURRENCY=1
+    concurrency=1
   fi
-  echo $WEB_CONCURRENCY
+  echo "$concurrency"
 }
 
 log_concurrency() {
@@ -26,6 +30,18 @@ detect_memory() {
   fi
 }
 
+bound_memory() {
+  local detected=$1
+  local detected max_detected_memory=14336
+
+  # The hardcoded value is 16GB of memory
+  if (( detected > max_detected_memory )); then
+    echo "$max_detected_memory"
+  else
+    echo "$detected"
+  fi
+}
+
 warn_bad_web_concurrency() {
   local concurrency=$((MEMORY_AVAILABLE/WEB_MEMORY))
   if [ "$concurrency" -gt "200" ]; then
@@ -39,9 +55,10 @@ appropriate for your application."
   fi
 }
 
-export MEMORY_AVAILABLE=${MEMORY_AVAILABLE-$(detect_memory 512)}
+DETECTED=$(detect_memory 512)
+export MEMORY_AVAILABLE=${MEMORY_AVAILABLE-$(bound_memory $DETECTED)}
 export WEB_MEMORY=${WEB_MEMORY-512}
-export WEB_CONCURRENCY=$(calculate_concurrency)
+export WEB_CONCURRENCY=$(calculate_concurrency $MEMORY_AVAILABLE $WEB_MEMORY)
 
 warn_bad_web_concurrency
 

test/unit

@@ -168,6 +168,48 @@ testBuildData() {
   assertEquals "a=\"this should come first\" foo=\"value with spaces\" test=different-foo" "$(log_build_data)"
 }
 
+testWebConcurrencyProfileScript() {
+  # this was set when we sourced the WEB_CONCURRENCY.sh file
+  unset WEB_MEMORY
+  unset MEMORY_AVAILABLE
+  unset WEB_CONCURRENCY
+
+  # memory in MB of a 2X dyno
+  assertEquals "512" "$(bound_memory 512)"
+
+  # memory in MB of a 2X dyno
+  assertEquals "1024" "$(bound_memory 1024)"
+
+  # memory in MB of a Peformance-M dyno
+  assertEquals "2560" "$(bound_memory 2560)"
+
+  # memory in MB of a Peformance-L dyno
+  assertEquals "14336" "$(bound_memory 14336)"
+
+  # one more MB
+  assertEquals "14336" "$(bound_memory 14337)"
+
+  # On non-Heroku systems `detect_memory` can return non-sensically large values
+  # In this case, we should bound
+  assertEquals "14336" "$(bound_memory 1000000)"
+
+  # test calculate_concurrency
+
+  # 1x
+  assertEquals "1" "$(calculate_concurrency 512 512)"
+  # 2x
+  assertEquals "2" "$(calculate_concurrency 1024 512)"
+  # Performance-M
+  assertEquals "5" "$(calculate_concurrency 2560 512)"
+  # Performance-L
+  assertEquals "28" "$(calculate_concurrency 14336 512)"
+
+  # In case some very large memory available value gets passed in
+  assertEquals "1" "$(calculate_concurrency 103401 512)"
+  # of if web memory is set really low
+  assertEquals "1" "$(calculate_concurrency 512 1)"
+}
+
 # mocks
 source "$(pwd)"/test/mocks/stdlib.sh
 
@@ -176,6 +218,7 @@ source "$(pwd)"/lib/monitor.sh
 source "$(pwd)"/lib/output.sh
 source "$(pwd)"/lib/kvstore.sh
 source "$(pwd)"/lib/build-data.sh
+source "$(pwd)"/profile/WEB_CONCURRENCY.sh
 
 # import the testing framework
 source "$(pwd)"/test/shunit2