check-mysql-replication-status: add lag flapping protection

Author: Jan Kunzmann

CHANGELOG.md

@@ -7,6 +7,7 @@ This CHANGELOG follows the format listed [here](https://github.com/sensu-plugins
 ### Changed
 - check-mysql-replication-status: fix code flow if server is not a slave (@DrMurx)
 - check-mysql-replication-status: refactoring & spec tests (@DrMurx)
+- check-mysql-replication-status: added flapping protection (@DrMurx)
 
 ## [3.1.0] - 2018-12-15
 ### Added

README.md

@@ -80,6 +80,15 @@ $ /opt/sensu/embedded/bin/check-mysql-threads.rb --host=<DBHOST> --ini=/etc/sens
 $ /opt/sensu/embedded/bin/check-mysql-replication-status.rb --host=<SLAVE> --ini=/etc/sensu/my.ini
 ```
 
+**check-mysql-replication-status** example with flapping protection
+
+MariaDB/MySQL sometimes wrongly reports a very high replication lag for a short moment. Flapping protection helps mitigating this issue
+better than setting `occurrences` in sensu's `checks` definition because you don't lose any alerting granularity.
+
+```bash
+$ /opt/sensu/embedded/bin/check-mysql-replication-status.rb --host=<SLAVE> --ini=/etc/sensu/my.ini --flapping-retry=1 --flapping-lag=86400 --flapping-sleep=2
+```
+
 **check-mysql-msr-replication-status** example
 ```bash
 $ /opt/sensu/embedded/bin/check-mysql-replication-status.rb --host=<SLAVE> --ini=/etc/sensu/my.ini

bin/check-mysql-replication-status.rb

@@ -94,6 +94,27 @@ class CheckMysqlReplicationStatus < Sensu::Plugin::Check::CLI
          # #YELLOW
          proc: lambda { |s| s.to_i } # rubocop:disable Lambda
 
+  option :flapping_lag,
+         short: '-l',
+         long: '--flapping-lag=VALUE',
+         description: 'Lag threshold to trigger flapping protection',
+         default: 100000,
+         proc: lambda { |s| s.to_i } # rubocop:disable Lambda
+
+  option :flapping_retry,
+         short: '-r',
+         long: '--flapping-retry=VALUE',
+         description: 'Number of retries when lag flapping protection is triggered',
+         default: 0,
+         proc: lambda { |s| s.to_i } # rubocop:disable Lambda
+
+  option :flapping_sleep,
+         long: '--flapping-sleep=VALUE',
+         description: 'Sleep between flapping protection retries',
+         default: 1,
+         proc: lambda { |s| s.to_i } # rubocop:disable Lambda
+
+
   def detect_replication_status?(row)
     %w[
       Slave_IO_State
@@ -175,19 +196,29 @@ def ok_slave_message
   def run
     db = open_connection
 
-    row = query_slave_status(db)
-    ok 'show slave status was nil. This server is not a slave.' if row.nil?
-    warn "couldn't detect replication status" unless detect_replication_status?(row)
-
-    slave_running = slave_running?(row)
-    critical broken_slave_message(row) unless slave_running
-
-    replication_delay = row['Seconds_Behind_Master'].to_i
-    message = "replication delayed by #{replication_delay}"
-    # TODO (breaking change): Thresholds are exclusive which is not consistent with all other checks
-    critical message if replication_delay > config[:crit]
-    warning message if replication_delay > config[:warn]
-    ok "#{ok_slave_message}, #{message}"
+    retries = config[:flapping_retry]
+    # Note: Endless loop will exit via `ok`, `warning` or `critical`, or by Exception
+    loop do
+      row = query_slave_status(db)
+      ok 'show slave status was nil. This server is not a slave.' if row.nil?
+      warn "couldn't detect replication status" unless detect_replication_status?(row)
+
+      slave_running = slave_running?(row)
+      critical broken_slave_message(row) unless slave_running
+
+      replication_delay = row['Seconds_Behind_Master'].to_i
+      retries -= 1
+      if replication_delay >= config[:flapping_lag] && retries >= 0
+        sleep config[:flapping_sleep]
+        next
+      end
+
+      message = "replication delayed by #{replication_delay}"
+      # TODO (breaking change): Thresholds are exclusive which is not consistent with all other checks
+      critical message if replication_delay > config[:crit]
+      warning message if replication_delay > config[:warn]
+      ok "#{ok_slave_message}, #{message}"
+    end
   rescue Mysql::Error => e
     errstr = "Error code: #{e.errno} Error message: #{e.error}"
     critical "#{errstr} SQLSTATE: #{e.sqlstate}" if e.respond_to?('sqlstate')

test/check-mysql-replication-status_spec.rb

@@ -52,10 +52,10 @@ def checker.critical(*_args)
     ['No',  'Yes',  nil, 2, 'critical'],
     ['Yes', 'No',   nil, 2, 'critical'],
     ['No',  'No',   nil, 2, 'critical'],
-    ['Yes', 'Yes',  899, 0, 'ok'],
-    ['Yes', 'Yes',  900, 1, 'warning'],
-    ['Yes', 'Yes', 1799, 1, 'warning'],
-    ['Yes', 'Yes', 1800, 2, 'critical'],
+    ['Yes', 'Yes',  900, 0, 'ok'],
+    ['Yes', 'Yes',  901, 1, 'warning'],
+    ['Yes', 'Yes', 1800, 1, 'warning'],
+    ['Yes', 'Yes', 1801, 2, 'critical'],
   ].each do |testdata|
     it "returns #{testdata[4]} for default thresholds" do
       slave_status_row = {
@@ -76,4 +76,38 @@ def checker.critical(*_args)
       expect(exit_code).to eq testdata[3]
     end
   end
+
+  it "sleeps with flapping protection for default thresholds" do
+    checker.config[:flapping_retry] = 1
+    checker.config[:flapping_sleep] = 10
+
+    slave_status_row = [
+      {
+        "Slave_IO_State" => '',
+        "Slave_IO_Running" => 'Yes',
+        "Slave_SQL_Running" => 'Yes',
+        "Last_IO_Error" => '',
+        "Last_SQL_Error" => '',
+        "Seconds_Behind_Master" => 100000
+      },
+      {
+        "Slave_IO_State" => '',
+        "Slave_IO_Running" => 'Yes',
+        "Slave_SQL_Running" => 'Yes',
+        "Last_IO_Error" => '',
+        "Last_SQL_Error" => '',
+        "Seconds_Behind_Master" => 99999
+      }
+    ]
+
+    begin
+      allow(checker).to receive(:open_connection) # do nothing
+      allow(checker).to receive(:query_slave_status).and_return slave_status_row[0], slave_status_row[1]
+      expect(checker).to receive(:sleep).with(10)
+      checker.run
+    rescue SystemExit => e
+      exit_code = e.status
+    end
+    expect(exit_code).to eq 2
+  end
 end