Allow scale down at 0%, fixes #17

dynamic_dynamodb/dynamic_dynamodb.py

@@ -49,6 +49,8 @@ def __init__(self, region, table_name,
                 increase_writes_with, decrease_writes_with,
                 min_provisioned_reads=None, max_provisioned_reads=None,
                 min_provisioned_writes=None, max_provisioned_writes=None,
+                allow_scaling_down_reads_on_0_percent=False,
+                allow_scaling_down_writes_on_0_percent=False,
                 check_interval=300, dry_run=True,
                 aws_access_key_id=None, aws_secret_access_key=None,
                 maintenance_windows=None, logger=None):
@@ -82,6 +84,12 @@ def __init__(self, region, table_name,
         :param min_provisioned_writes: Minimum number of provisioned writes
         :type max_provisioned_writes: int
         :param max_provisioned_writes: Maximum number of provisioned writes
+        :type allow_scaling_down_reads_on_0_percent: bool
+        :param allow_scaling_down_reads_on_0_percent:
+            Allow scaling when 0 percent of the reads are consumed
+        :type allow_scaling_down_writes_on_0_percent: bool
+        :param allow_scaling_down_writes_on_0_percent:
+            Allow scaling when 0 percent of the writes are consumed
         :type check_interval: int
         :param check_interval: How many seconds to wait between checks
         :type dry_run: bool
@@ -129,6 +137,10 @@ def __init__(self, region, table_name,
         self.aws_access_key_id = aws_access_key_id
         self.aws_secret_access_key = aws_secret_access_key
         self.maintenance_windows = maintenance_windows
+        self.allow_scaling_down_reads_on_0_percent = \
+            allow_scaling_down_reads_on_0_percent
+        self.allow_scaling_down_writes_on_0_percent = \
+            allow_scaling_down_writes_on_0_percent
 
         if min_provisioned_reads:
             self.min_provisioned_reads = int(min_provisioned_reads)
@@ -165,7 +177,8 @@ def ensure_proper_provisioning(self):
         }
 
         # Check if we should update read provisioning
-        if read_usage_percent == 0:
+        if read_usage_percent == 0 and not \
+           self.allow_scaling_down_reads_on_0_percent:
             self.logger.info(
                 'Scaling down reads is not done when usage is at 0%')
         elif read_usage_percent >= self.reads_upper_threshold:
@@ -183,7 +196,8 @@ def ensure_proper_provisioning(self):
             throughput['read_units'] = new_value
 
         # Check if we should update write provisioning
-        if write_usage_percent == 0:
+        if write_usage_percent == 0 and not \
+           self.allow_scaling_down_writes_on_0_percent:
             self.logger.info(
                 'Scaling down writes is not done when usage is at 0%')
         elif write_usage_percent >= self.writes_upper_threshold:

dynamic_dynamodb/main.py

@@ -164,6 +164,8 @@ def main():
         config['max-provisioned-reads'] = args.max_provisioned_reads
         config['min-provisioned-writes'] = args.min_provisioned_writes
         config['max-provisioned-writes'] = args.max_provisioned_writes
+        config['allow-scaling-down-reads-on-0-percent'] = False
+        config['allow-scaling-down-writes-on-0-percent'] = False
         config['check-interval'] = args.check_interval
         config['aws-access-key-id'] = args.aws_access_key_id
         config['aws-secret-access-key'] = args.aws_secret_access_key
@@ -197,6 +199,8 @@ def main():
                 config['max-provisioned-reads'],
                 config['min-provisioned-writes'],
                 config['max-provisioned-writes'],
+                config['allow-scaling-down-reads-on-0-percent'],
+                config['allow-scaling-down-writes-on-0-percent'],
                 check_interval=config['check-interval'],
                 dry_run=config['dry-run'],
                 aws_access_key_id=config['aws-access-key-id'],
@@ -227,6 +231,8 @@ def main():
             config['max-provisioned-reads'],
             config['min-provisioned-writes'],
             config['max-provisioned-writes'],
+            config['allow-scaling-down-reads-on-0-percent'],
+            config['allow-scaling-down-writes-on-0-percent'],
             check_interval=config['check-interval'],
             dry_run=config['dry-run'],
             aws_access_key_id=config['aws-access-key-id'],
@@ -341,19 +347,31 @@ def parse_configuration_file(config_path):
         ('max-provisioned-reads', False),
         ('min-provisioned-writes', False),
         ('max-provisioned-writes', False),
-        ('maintenance-windows', False)
+        ('maintenance-windows', False),
+        ('allow-scaling-down-reads-on-0-percent', False),
+        ('allow-scaling-down-writes-on-0-percent', False),
     ]
 
     # Populate the table options
     for option, required in table_options:
         try:
-            config[option] = config_file.get(section, option)
+            if option == 'allow-scaling-down-reads-on-0-percent':
+                config[option] = config_file.getboolean(section, option)
+            elif option == 'allow-scaling-down-writes-on-0-percent':
+                config[option] = config_file.getboolean(section, option)
+            else:
+                config[option] = config_file.get(section, option)
         except ConfigParser.NoOptionError:
             if required:
                 print 'Missing [{0}] option "{1}" in {2}'.format(
                     section, option, config_path)
                 sys.exit(1)
             else:
-                config[option] = None
+                if option == 'allow-scaling-down-reads-on-0-percent':
+                    config[option] = False
+                elif option == 'allow-scaling-down-writes-on-0-percent':
+                    config[option] = False
+                else:
+                    config[option] = None
 
     return config

example-dynamic-dynamodb.conf

@@ -56,3 +56,11 @@ decrease-writes-with: 50
 # Maintenance windows (in UTC)
 #
 #maintenance-windows: 22:00-23:59,00:00-06:00
+
+#
+# Other settings
+#
+
+# Allow down scaling when at 0% consumed reads
+#allow-scaling-down-reads-on-0-percent: true
+#allow-scaling-down-writes-on-0-percent: true