Merge pull request #164 from GSA/system-description-doc

Add a system description entry to docs

docs/system-description.md

@@ -0,0 +1,38 @@
+US Notify
+=========
+
+System Description
+------------------
+
+US Notify is a service being developed by the TTS Public Benefits Studio to increase the availability of
+SMS and email notifications to Federal, State, and Local Benefits agencies.
+
+Agencies that sign up will be able to create and use personalized message templates for sending
+notifications to members of the public regarding their benefits. These could include reminders
+about upcoming enrollment deadlines and tasks, or information about upcoming appointments, events,
+or services.
+
+The templates are sent by the agency using one of two methods:
+
+* using the US Notify API to send a message to a given recipient with given personalization values
+* using the US Notify website to upload a CSV file of recipients and their personalization values, one row per message
+
+### Environment
+
+US Notify is comprised of two applications both running on cloud.gov:
+
+* Admin, a Flask website running on the python_buildpack which hosts agency user-facing UI
+* API, a Flask application running on the python_buildpack hosting the US Notify API
+
+US Notify utilizes several cloud.gov-provided services:
+
+* S3 buckets for temporary file storage
+* Elasticache (redis) for cacheing data and enqueueing background tasks
+* RDS (PostgreSQL) for system data storage
+
+US Notify also provisions and uses two AWS services via a [supplemental service broker](https://github.com/GSA/datagov-ssb):
+
+* [SNS](https://aws.amazon.com/sns/) for sending SMS messages
+* [SES](https://aws.amazon.com/ses/) for sending email messages
+
+For further details of the system and how it connects to supporting services, see the [application boundary diagram](https://github.com/GSA/us-notify-compliance/blob/main/diagrams/rendered/apps/application.boundary.png)