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brodie.id.au/blog/serverless-investment-management-portfolio.md

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+```{post} 22 November, 2024
+:author: Brodie Blackburn
+```
+# Serverless investment management portfolio
+
+```{figure} portfolio-demo.png
+:alt: Index worksheet
+
+[portfolio-demo.brodie.id.au](https://portfolio-demo.brodie.id.au)
+```
+
+I built a system that helps manage investments.
+
+It does the following things:
+- Automatically retrieves account balances and asset prices from various financial institutions.
+- Maintains an ever-increasing ledger of balances over time.
+- Creates a database containing asset values normalised to an AUD basis.
+- Delegates painful emotional decisions to a robot.
+- Executes a pre-determined portfolio strategy to determine how to re-orient (you still have to pull the trigger).
+- Builds a single pane of glass showing key stats.
+- Deploys to AWS for approximately 0 dollars (except maybe 50c per month if you don't already have a Route 53 zone).
+
+You can check out a demo with example data [here](https://portfolio-demo.brodie.id.au),
+and view source code [here](https://github.com/eidorb/portfolio).
+
+
+## Investment strategy
+
+I realised cash savings are *guaranteed* to lose value over time.
+I needed to take on some risk.
+The timeframe is long-term, however.
+There are *guaranteed* to be ups and downs. Volatility.
+
+If the goal is long-term than this system better be hands-off, simple and not psychologically difficult.
+I've decided on some allocation between risky and less risky asset classes. The mix of which is in accordance with my personal risk tolerance.
+
+This Bogle fella has some interesting [ideas](https://www.bogleheads.org/wiki/Rebalancing).
+
+
+## The system
+
+Several times a month, GitHub Actions triggers automated workflows.
+
+
+## A plain-text ledger
+
+Balances are written to a Beancount ledger (it's just a text file).
+With Beancount you'd typically track *all* of your transactions, not just balances.
+Usually the hard work is all in categorising transactions.
+If we stick to just balances, it's pretty simple to automate.
+
+Sometimes automatic retrieval breaks.
+These shitty bank websites change all the time 🤣!
+(At least there's [Up](https://developer.up.com.au).)
+
+Beancount ledgers are easily updated by hand. Balance entries looks like this:
+
+```
+2023-11-26 balance Assets:Bank:Savings                              20000.0 AUD
+2023-11-26 balance Liabilities:Bank:CreditCard                     -5000.0 AUD
+```
+
+It's simple to add manual entries until there's time to rework the retrieval code.
+
+Simon Willison's concept of [Git scraping](https://simonwillison.net/2020/Oct/9/git-scraping/) is pretty cool!
+Just keeping data in plain text files.
+Updates are infrequent enough so it simply rebuilds the database and website every update.
+GitHub Actions can make git commits on your behalf so your ledger stays up-to-date 💃.
+
+Oh, and if those Fort Knox banks (secured with single-factor authentication) try to block your connections originating from GitHub's ASN, you can just re-route your "hacking" via home using a lightweight [VPN](https://tailscale.com)!
+
+
+## Infrastructure costs
+
+Scaling to zero is economical.
+
+The website will have many dozens of views per month.
+It's not running when you're not looking at it.
+It turns out you can wrap entire Python web applications with a Lambda Function.
+
+The downside is potentially having to wait a needless couple of hundred milliseconds.
+
+
+## Security
+
+I should be in control of who sees my financial information. There's a [Datasette plugin](https://datasette.io/plugins/datasette-auth-github) that handles this.