[Bps-public-commit] app-aws-cloudwatch-monitor branch 0.03/update-meta-data-caching-writes created. bf14385889a4699ca0ea58731bd419e548e0aabd

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The branch, 0.03/update-meta-data-caching-writes has been created
        at  bf14385889a4699ca0ea58731bd419e548e0aabd (commit)

- Log -----------------------------------------------------------------
commit bf14385889a4699ca0ea58731bd419e548e0aabd
Author: Blaine Motsinger <blaine at bestpractical.com>
Date:   Thu May 19 13:30:35 2022 -0500

    Fix meta-data caching writes
    
    The meta-data cache files are written after every call, regardless
    of the TTL variables.  This presents a couple issues.
    
    First, the age of the cache files never get older than the time of
    the last call, effectively making the TTL time meaningless.  This
    leads to far too many unnecessary writes to the disk since the
    cache files never age.
    
    Second, since the TTL time is not honored, if the special meta-data
    mount is incorrectly returning empty string (an issue at AWS or the
    mount on the instance), the benefit of relying on a cached value is
    lost.
    
    This commit fixes the meta-data cache writes to now only write the
    cache file if a value was retrieved from the special mount, which
    only happens if the TTL is reached or the cache file doesn't exist
    or doesn't contain a value.

diff --git a/lib/App/AWS/CloudWatch/Monitor/CloudWatchClient.pm b/lib/App/AWS/CloudWatch/Monitor/CloudWatchClient.pm
index 21c8845..bdbcaa4 100644
--- a/lib/App/AWS/CloudWatch/Monitor/CloudWatchClient.pm
+++ b/lib/App/AWS/CloudWatch/Monitor/CloudWatchClient.pm
@@ -124,18 +124,22 @@ sub get_meta_data {
     my $use_cache = shift;
     my $meta_data = read_meta_data( $resource, $meta_data_short_ttl );
 
-    my $base_uri   = 'http://169.254.169.254/latest/meta-data';
-    my $data_value = !$meta_data ? get $base_uri. $resource : $meta_data;
+    # if we didn't get meta data from the cache (it might not exist, or the cache TTL expired),
+    # get the meta data from the meta-data mount.
+    unless ($meta_data) {
+        my $base_uri   = 'http://169.254.169.254/latest/meta-data';
+        my $data_value = get $base_uri . $resource;
 
-    if ( !$data_value ) {
-        return "";
-    }
+        if ($data_value) {
+            $meta_data = $data_value;
 
-    if ($use_cache) {
-        write_meta_data( $resource, $data_value );
+            if ($use_cache) {
+                write_meta_data( $resource, $data_value );
+            }
+        }
     }
 
-    return $data_value;
+    return $meta_data;
 }
 
 =item read_meta_data
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