Cases2 cases

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1. IL-0573 A developer's mistake dropped nine main tables of the Baemin billing MariaDB database and payments briefly stopped

   Woowa Brothers2016

   Symptoms

   At 15:00 on 27 December 2016, while a developer was working on a payment system module, nine main tables of the billing database were dropped. The monitoring system turned red, failure alerts poured in, and payments in 배달의민족 (Baemin) stopped for a while.

   Data lossService outage

   Trigger

   While developing a payment system module, the developer who wrote the post dropped nine main tables of the billing database by mistake.

   Root cause

   Operator error

   Component

   DatabaseDatabase backups and snapshots

   Contributing factor

   –

   Detection

   The monitoring system turned red and failure alerts fired.

   Remediation

   • Pointed the application at a temporary database, which kept the outage short
   • Restored the dropped tables from the 6:00 mysqldump full backup
   • Replayed the binary log from 6:00 to 15:00 with mysqlbinlog, filtered to the nine tables and stopping before the DROP TABLE

   Action items

   • Replace mysqldump backups of the billing database with full backups taken by XtraBackup

   Lessons

   There are many points where such failures can be managed: separate database accounts for the service and for administration, check once more before running a query, and guard against rm -rf. Without the full backup and the binary log the data could not have been recovered, so every team should check that it has a full recovery point for a failure.

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2. IL-0454 Baemin billing servers could not open new MariaDB connections at the start of a card-discount event

   Woowa Brothers2016

   Symptoms

   At 18:00, when a card-company event giving 3,000 won off to the first 1,000 customers started, the Pinpoint graph of the Baemin billing system turned red shortly afterwards: 140 of 14,000 requests failed in about one minute. Most errors looked like requests from the billing system that the payment gateway (PG) did not receive because of a network problem, but other errors pointed at the billing system itself.

   High error rateIntermittent connection failures

   Trigger

   A card-company discount event for the first 1,000 customers started at 18:00 and sent about 14,000 requests to the billing system in about one minute.

   Root cause

   Software defect

   Component

   DatabaseClient-side DNS resolver and cache

   Contributing factor

   Unpatched known bug

   Detection

   The team was watching NewRelic and Pinpoint during the 18:00 event, and the Pinpoint graph turned red shortly after the event began.

   Remediation

   • Changed the Gradle settings to use mariadb-connector-j 1.5.5 instead of 1.4.6

   Lessons

   A new DB connection failed because the driver did a DNS lookup of the local host name that took about 6 seconds, longer than the server's 5-second connect_timeout. Other ways to avoid it are to use localhost as the host name or to register the IP address and host name in /etc/hosts so the address is returned first. Above all, the author recommends keeping libraries on recent versions.

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