jjankowiak jjankowiak - 1 year ago 309
MySQL Question

docker-compose Unknown MySQL server host 'mysql' (airflow)

I try to create my Airflow service. When I run three dockers separately (without

) everything works but when I try to do the same using
I get the error. It seems that airflow doesn't see database.


version: '2'


image: "someregisty/mysql"
- MYSQL_ROOT_PASSWORD=somepassword

image: "someregisty/redis"

image: "someregisty/airflow"
- ./dags:/home/airflow/dags
- ./logs:/home/airflow/logs
- ./config/airflow.cfg:/home/airflow/airflow.cfg
- ./config/resolv.conf:/etc/resolv.conf
- ./config/somekeytab.keytab:/home/airflow/airflow.keytab
- "8484:8080"
- AIRFLOW__CELERY__BROKER_URL=redis://redis:6379/0
- AIRFLOW__CELERY__CELERY_RESULT_BACKEND=db+mysql://root:[email protected]/airflow
- AIRFLOW__CORE__SQL_ALCHEMY_CONN=mysql://root:[email protected]/airflow
- AIRFLOW__CORE__DAGS_FOLDER=/home/airflow/dags/
- AIRFLOW__CORE__PLUGINS_FOLDER=/home/airflow/plugins/
- [email protected]
- AIRFLOW__KERBEROS__CCACHE=/home/airflow/kerberos.keytab.cache
- KRB5CCNAME=/home/airflow/kerberos.keytab.cache
- redis
- mysql

I run

docker-compose up -d
docker-compose exec mysql mysql -u root --password=somepassword -e "create database airflow"

and that works ok. Then I run

docker-compose exec airflow airflow initdb

And I get

[2017-09-28 16:34:36,100] {__init__.py:57} INFO - Using executor CeleryExecutor
/usr/lib/python2.7/site-packages/airflow/utils/helpers.py:406: DeprecationWarning: Importing BaseSensorOperator directly from <module 'airflow.operators' from '/usr/lib/python2.7/site-packages/airflow/operators/__init__.pyc'> has been deprecated. Please import from '<module 'airflow.operators' from '/usr/lib/python2.7/site-packages/airflow/operators/__init__.pyc'>.[operator_module]' instead. Support for direct imports will be dropped entirely in Airflow 2.0.
DB: mysql://root:***@mysql/airflow
[2017-09-28 16:34:36,666] {db.py:287} INFO - Creating tables
Traceback (most recent call last):
File "/usr/bin/airflow", line 28, in <module>
File "/usr/lib/python2.7/site-packages/airflow/bin/cli.py", line 951, in initdb
File "/usr/lib/python2.7/site-packages/airflow/utils/db.py", line 106, in initdb
File "/usr/lib/python2.7/site-packages/airflow/utils/db.py", line 294, in upgradedb
command.upgrade(config, 'heads')
File "/usr/lib/python2.7/site-packages/alembic/command.py", line 174, in upgrade
File "/usr/lib/python2.7/site-packages/alembic/script/base.py", line 416, in run_env
util.load_python_file(self.dir, 'env.py')
File "/usr/lib/python2.7/site-packages/alembic/util/pyfiles.py", line 93, in load_python_file
module = load_module_py(module_id, path)
File "/usr/lib/python2.7/site-packages/alembic/util/compat.py", line 79, in load_module_py
mod = imp.load_source(module_id, path, fp)
File "/usr/lib/python2.7/site-packages/airflow/migrations/env.py", line 86, in <module>
File "/usr/lib/python2.7/site-packages/airflow/migrations/env.py", line 73, in run_migrations_online
with connectable.connect() as connection:
File "/usr/lib64/python2.7/site-packages/sqlalchemy/engine/base.py", line 2091, in connect
return self._connection_cls(self, **kwargs)
File "/usr/lib64/python2.7/site-packages/sqlalchemy/engine/base.py", line 90, in __init__
if connection is not None else engine.raw_connection()
File "/usr/lib64/python2.7/site-packages/sqlalchemy/engine/base.py", line 2177, in raw_connection
self.pool.unique_connection, _connection)
File "/usr/lib64/python2.7/site-packages/sqlalchemy/engine/base.py", line 2151, in _wrap_pool_connect
e, dialect, self)
File "/usr/lib64/python2.7/site-packages/sqlalchemy/engine/base.py", line 1465, in _handle_dbapi_exception_noconnection
File "/usr/lib64/python2.7/site-packages/sqlalchemy/util/compat.py", line 203, in raise_from_cause
reraise(type(exception), exception, tb=exc_tb, cause=cause)
File "/usr/lib64/python2.7/site-packages/sqlalchemy/engine/base.py", line 2147, in _wrap_pool_connect
return fn()
File "/usr/lib64/python2.7/site-packages/sqlalchemy/pool.py", line 328, in unique_connection
return _ConnectionFairy._checkout(self)
File "/usr/lib64/python2.7/site-packages/sqlalchemy/pool.py", line 766, in _checkout
fairy = _ConnectionRecord.checkout(pool)
File "/usr/lib64/python2.7/site-packages/sqlalchemy/pool.py", line 516, in checkout
rec = pool._do_get()
File "/usr/lib64/python2.7/site-packages/sqlalchemy/pool.py", line 1138, in _do_get
File "/usr/lib64/python2.7/site-packages/sqlalchemy/util/langhelpers.py", line 66, in __exit__
compat.reraise(exc_type, exc_value, exc_tb)
File "/usr/lib64/python2.7/site-packages/sqlalchemy/pool.py", line 1135, in _do_get
return self._create_connection()
File "/usr/lib64/python2.7/site-packages/sqlalchemy/pool.py", line 333, in _create_connection
return _ConnectionRecord(self)
File "/usr/lib64/python2.7/site-packages/sqlalchemy/pool.py", line 461, in __init__
File "/usr/lib64/python2.7/site-packages/sqlalchemy/pool.py", line 651, in __connect
connection = pool._invoke_creator(self)
File "/usr/lib64/python2.7/site-packages/sqlalchemy/engine/strategies.py", line 105, in connect
return dialect.connect(*cargs, **cparams)
File "/usr/lib64/python2.7/site-packages/sqlalchemy/engine/default.py", line 393, in connect
return self.dbapi.connect(*cargs, **cparams)
File "/usr/lib64/python2.7/site-packages/MySQLdb/__init__.py", line 86, in Connect
return Connection(*args, **kwargs)
File "/usr/lib64/python2.7/site-packages/MySQLdb/connections.py", line 204, in __init__
super(Connection, self).__init__(*args, **kwargs2)
sqlalchemy.exc.OperationalError: (_mysql_exceptions.OperationalError) (2005, "Unknown MySQL server host 'mysql' (0)")

I don't know what is wrong. Maybe you could help me? :)

Versions of docker and docker-compose are

Docker version 1.12.6, build 96d83a5/1.12.6
docker-compose version 1.9.0, build 2585387

Answer Source

The problem is caused by binding resolv.conf file into airflow container. The reason you get unknown MySQL server host 'mysql' error from airflow container is that mysql hostname does not resolve to the ip of airflow container.

Solution 1

Remove ./config/resolv.conf:/etc/resolv.conf from Compose configuration. It will cause Docker to resolve hostname correctly. If you need to specify additional DNS servers use Compose --dns option documented here.

Solution 2 (not recommended)

Add nameserver line to /etc/resolv.conf file. It enables usage of Docker embedded DNS server, which is a default setup. You can keep your custom entries in that file as well. Note that this solution is a hack because, as stated in documentation, Docker is responsible for managing /etc/resolv.conf file. Quote from documentation to back it up:

So you should not assume the way the files such as /etc/hosts, /etc/resolv.conf are managed inside the containers and leave the files alone and use the following Docker options instead


You can read more about Docker embedded DNS server in user-defined networks here.

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