[AIRFLOW-3288] Add SNS integration

[sjednac]

Jira

• My PR addresses the following Airflow Jira issues and references them in the PR title. For example, "[AIRFLOW-XXX] My Airflow PR"
  • https://jira.apache.org/jira/browse/AIRFLOW-3288

Description

• Here are some details about my PR, including screenshots of any UI changes:

Adds a hook and a basic operator for publishing Amazon SNS messages.

Our project is currently using an identical plugin for integrating SQS into our Airflow pipelines, but it could be used for other purposes as well (e-mail, sms, lambda function invocation etc.).

Tests

• My PR adds the following unit tests OR does not need testing for this extremely good reason:

The hook and the operator have independent unit tests.

Commits

• My commits all reference Jira issues in their subject lines, and I have squashed multiple commits if they address the same issue. In addition, my commits follow the guidelines from "How to write a good git commit message":
  1. Subject is separated from body by a blank line
  2. Subject is limited to 50 characters (not including Jira issue reference)
  3. Subject does not end with a period
  4. Subject uses the imperative mood ("add", not "adding")
  5. Body wraps at 72 characters
  6. Body explains "what" and "why", not "how"

Documentation

• In case of new functionality, my PR adds documentation that describes how to use it.
  • When adding new operators/hooks/sensors, the autoclass documentation generation needs to be added.

Classes and methods should be documented.

Code Quality

• Passes flake8

[codecov-io]

Codecov Report

Merging #4123 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #4123   +/-   ##
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  Coverage   76.66%   76.66%           
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  Files         199      199           
  Lines       16209    16209           
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  Hits        12427    12427           
  Misses       3782     3782

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[msumit]

lgtm

[ashb]

These new classes are not linked from the docs - please add them to at least docs/code.rst

[sjednac]

@ashb

1. Sorry about that - I'm going to open a PR fixing this shortly.
2. I'd suggest to include this info in the PR template, as the following is not clear enough in my opinion:

When adding new operators/hooks/sensors, the autoclass documentation generation needs to be added