Apache Airflow version:

1.10.12

Kubernetes version (if you are using kubernetes) (use kubectl version):

n/a

Environment:

• Cloud provider or hardware configuration:
  Amazon MWAA

• OS (e.g. from /etc/os-release):
  Amazon Linux (latest)

• Kernel (e.g. uname -a):
  n/a

• Install tools:
  n/a

What happened:

If an unreachable secrets.backend is specified in airflow.cfg the web server crashes

What you expected to happen:

An invalid secrets backend should be ignored with a warning, and the system should default back to the metadatabase secrets

How to reproduce it:

In an environment without access to AWS Secrets Manager, add the following to your airflow.cfg:

[secrets]
backend = airflow.contrib.secrets.aws_secrets_manager.SecretsManagerBackend

or an environment without access to SSM specifiy:

[secrets]
backend = airflow.contrib.secrets.aws_systems_manager.SystemsManagerParameterStoreBackend

Reference: https://airflow.apache.org/docs/apache-airflow/1.10.12/howto/use-alternative-secrets-backend.html#aws-ssm-parameter-store-secrets-backend