title: Airflow initdb failed in Amazon Linux
body: <p>I am trying to install Airflow in EC2 (Amazon Linux) and "airflow initdb" fails with the following error:</p>
  
  <pre><code>$ AIRFLOW_HOME=/var/lib/airflow airflow initdb
  [2019-09-07 20:51:32,416] {__init__.py:51} INFO - Using executor SequentialExecutor
  Traceback (most recent call last):
    File "/bin/airflow", line 22, in &lt;module&gt;
      from airflow.bin.cli import CLIFactory
    File "/usr/lib/python2.7/site-packages/airflow/bin/cli.py", line 68, in &lt;module&gt;
      from airflow.www_rbac.app import cached_app as cached_app_rbac
    File "/usr/lib/python2.7/site-packages/airflow/www_rbac/app.py", line 26, in &lt;module&gt;
      from flask_appbuilder import AppBuilder, SQLA
    File "/usr/lib/python2.7/site-packages/flask_appbuilder/__init__.py", line 5, in &lt;module&gt;
      from .base import AppBuilder
    File "/usr/lib/python2.7/site-packages/flask_appbuilder/base.py", line 5, in &lt;module&gt;
      from .api.manager import OpenApiManager
    File "/usr/lib/python2.7/site-packages/flask_appbuilder/api/__init__.py", line 11, in &lt;module&gt;
      from marshmallow_sqlalchemy.fields import Related, RelatedList
    File "/usr/lib/python2.7/site-packages/marshmallow_sqlalchemy/__init__.py", line 1, in &lt;module&gt;
      from .schema import TableSchemaOpts, ModelSchemaOpts, TableSchema, ModelSchema
    File "/usr/lib/python2.7/site-packages/marshmallow_sqlalchemy/schema.py", line 101
      class TableSchema(ma.Schema, metaclass=TableSchemaMeta):
                                        ^
  SyntaxError: invalid syntax
  </code></pre>
  
  <p>Since this is a syntax error, I suspect there is some version conflict between marshmallow_sqlalchemy and SQLAlchemy. Here are their versions:</p>
  
  <pre><code>apache-airflow==1.10.5
  Flask==1.1.1
  Flask-SQLAlchemy==2.4.0
  marshmallow==2.20.3
  marshmallow-enum==1.5.1
  marshmallow-sqlalchemy==0.19.0
  SQLAlchemy==1.3.8
  </code></pre>
  
  <p>Any idea?</p>