Implement MySQL check script for Docker

Story: 2001694
Task: 23321

Change-Id: I103c864832cd85ec528080cb7d49393c09127c60

docker/Dockerfile

@@ -5,7 +5,7 @@
 # https://github.com/pyca/cryptography/pull/4270
 FROM python:3.5.5-alpine3.7
 
-COPY wait_for.sh kafka_wait_for_topics.py /
+COPY wait_for.sh kafka_wait_for_topics.py mysql_check.py /
 COPY ashrc /root/.ashrc
 
 ENV \
@@ -23,7 +23,7 @@ LABEL org.opencontainers.image.revision="$BASE_GIT_COMMIT"
 LABEL org.opencontainers.image.licenses="Apache-2.0"
 
 RUN \
-    chmod +x /wait_for.sh /kafka_wait_for_topics.py && \
+    chmod +x /wait_for.sh /kafka_wait_for_topics.py /mysql_check.py && \
     apk add --no-cache \
         su-exec=0.2-r0 \
         tini=0.16.1-r0 \

docker/mysql_check.py

@@ -19,15 +19,34 @@
 
 It's checking if requested database already exists.
 
+For using this script you need to set some environment variables:
+* `MYSQL_HOST` for connection string to MySQL.
+  Example: `mysql`, `192.168.10.6`.
+  Default: `mysql`.
+* `MYSQL_PORT` for connection string to MySQL port.
+  Default: `3306`.
+* `MYSQL_USER` for user that is cappable to connect to MySQL.
+  Default: `monapi`.
+* `MYSQL_PASSWORD` for user password.
+  Default: `password`.
+* `MYSQL_DB` for database that you need to have before starting service.
+  Default: `mon`.
+
 After making sure that this environment variables are set you can simply
 execute this script in the following way:
 `python3 mysql_check.py && ./start_service.sh`
 `python3 mysql_check.py || exit 1`
+
+Additional environment variables available are:
+* `LOG_LEVEL` - default to `INFO`
+* `MYSQL_WAIT_RETRIES` - number of retries, default to `24`
+* `MYSQL_WAIT_INTERVAL` - in seconds, default to `5`
 """
 
 import logging
 import os
 import sys
+import time
 
 import pymysql
 
@@ -42,7 +61,7 @@ logging.basicConfig(level=LOG_LEVEL)
 logger = logging.getLogger(__name__)
 
 MYSQL_HOST = os.environ.get('MYSQL_HOST', 'mysql')
-MYSQL_PORT = os.environ.get('MYSQL_HOST', 3306)
+MYSQL_PORT = os.environ.get('MYSQL_PORT', 3306)
 MYSQL_USER = os.environ.get('MYSQL_USER', 'monapi')
 MYSQL_PASSWORD = os.environ.get('MYSQL_PASSWORD', 'password')
 MYSQL_DB = os.environ.get('MYSQL_DB', 'mon')
@@ -50,9 +69,64 @@ MYSQL_DB = os.environ.get('MYSQL_DB', 'mon')
 MYSQL_WAIT_RETRIES = int(os.environ.get('MYSQL_WAIT_RETRIES', '24'))
 MYSQL_WAIT_INTERVAL = int(os.environ.get('MYSQL_WAIT_INTERVAL', '5'))
 
-# TODO(Dobroslaw): All checks and retry.
-db = pymysql.connect(
-    host=MYSQL_HOST, port=MYSQL_PORT,
-    user=MYSQL_USER, passwd=MYSQL_PASSWORD,
-    db=MYSQL_DB
-)
+
+def retry(retries=MYSQL_WAIT_RETRIES, delay=MYSQL_WAIT_INTERVAL,
+          check_exceptions=()):
+    """Retry decorator."""
+    def decorator(func):
+        """Decorator."""
+        def f_retry(*args, **kwargs):
+            """Retry running function on exception after delay."""
+            for i in range(1, retries + 1):
+                try:
+                    return func(*args, **kwargs)
+                # pylint: disable=W0703
+                # We want to catch all exceptions here to retry.
+                except check_exceptions + (Exception,) as exc:
+                    if i < retries:
+                        logger.info('Connection attempt %d of %d failed',
+                                    i, retries)
+                        if isinstance(exc, check_exceptions):
+                            logger.debug('Caught known exception, retrying...',
+                                         exc_info=True)
+                        else:
+                            logger.warn(
+                                'Caught unknown exception, retrying...',
+                                exc_info=True)
+                    else:
+                        logger.exception('Failed after %d attempts', retries)
+
+                        raise
+
+                # No exception so wait before retrying
+                time.sleep(delay)
+
+        return f_retry
+    return decorator
+
+
+@retry(check_exceptions=(pymysql.err.OperationalError,))
+def connect_mysql(host, port, user, password, database):
+    """Connect to MySQL with retries."""
+    return pymysql.connect(
+        host=host, port=port,
+        user=user, passwd=password,
+        db=database
+    )
+
+
+def main():
+    """Start main part of the wait script."""
+    logger.info('Waiting for database: `%s`', MYSQL_DB)
+
+    connect_mysql(
+        host=MYSQL_HOST, port=MYSQL_PORT,
+        user=MYSQL_USER, password=MYSQL_PASSWORD,
+        database=MYSQL_DB
+    )
+
+    logger.info('Database `%s` found', MYSQL_DB)
+
+
+if __name__ == '__main__':
+    main()