General Lambda root readme

Lambdas/README.md

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+
+## Components
+### APIs
+Contains logic to retrieve data from merchant APIs.
+
+### Lists
+Contains client-facing Lambdas which are typically a rather thin wrapper over the database (MariaDB on AWS's RDS service) and other AWS services.
+#### General Client-facing Serverside Flow
+```
+Client -> API Gateway endpoint -> Lambda  -> (same) API Gateway endpoint -> (same) Client
+            |         .           |    .
+           \ /       / \         \ /  / \
+            '         |           '    |  
+           AWS Cognito          MariaDB instance/Other AWS services(SES, Cognito)
+```
+
+### Scraping
+Contains logic to orchestrate runs using a scraping utility to collect merchant data and store it in the database
+
+
+
+
+## Common Troubleshooting
+#### Logs
+- Logs may be written to by printing to the stdout. (Fancier logging is also possible, but currently not implemented)
+- Logs are avalaible on AWS's Cloudwatch under Log Groups -> {Lambda name}
+- Logs typically persist after deletion of the associated Lambda
+
+#### Incomplete runs
+Often if a run fails to complete, it is because the standard allocated time and memory/cpu is inadaquate.
+- Symptoms:
+  - The running time (available in the Cloudwatch logs) is almost exactly the maximum time.
+- Resolutions:
+  - Time may be increased.
+  - CPU may be increased. CPU is proportional to memory, so CPU is increased by increasing memory allocation.