Selecting database for building highly scalable and available URL shortner service

We want to build a URL shortening service.

Design goals :

a) Scalable

b) Highly available

I was analysing which type and specifically which database to use for the purpose.

a) Relational DB : Rejected

- Data is not relational   - SQL DB with ACID compliance is hard to scale  

b) Graph DB : Rejected

- Data model is not inherently graphical  

c) Persistent Key-value store : An option

- Most of the DB queries would be around slug   - It is faster to read from a key-value store due to limited   - Analytics will be taken care of separately   - The clustered mode will be easy to scale 

d) Document Store : An option

- Scalable   - Queries from various fields of a document are supported   - Data is not nested  

Based on the mentioned points, persistent Key-value store should be the best option for the same.

Can someone please help me out, if I missed anything in the consideration or if I may be wrong here. It would be of help.

If a persistent key-value store is best available option, then what is the correct way to select amongst the available options (REDIS, Couchbase, Aerospike, etc)

Best architecture for a web app with highly sensitive data

I have to design a web app that contains medical information. Only the staff of the organization need to access the data in the office and on the go. A VPN is already in place. On premise server management is outsourced to a company with limited knowledge on running web servers. Still, the client is very worried about putting any data on the cloud.

What is the best way to architect the app (Angular, Python backend, database) to secure the data?

These are the options I have thought of before:

  1. Host everything on premise behind a firewall, users will have use their VPN to log in. Pro: most secure. Con: their hosting will not be as cheap and efficient as something in the cloud.
  2. Host the Angular app in the cloud, and the Python backend and the database on premise. A static IP could be used for the Angular app and the firewall sitting on top of the backend could filter all traffic that doesn’t come from that IP to offer security on top of user authentication. Pro: Easier deployment for front end changes, access without using VPN possible, less hosting trouble, password to database would never reach the cloud. Con: hosting the backend on premise will still be an issue for a company with limited experience in this area.
  3. Host the Angular app and the Python backend in the cloud with a static IP. The database is on premise and the firewall filters all traffic that doesn’t come from the Python backend. Pro: Easier deployment, cheaper and more reliable hosting. Con: the password to the database connection lies in the cloud.

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What to do when Euler Lagrange Equation is highly nonlinear ode?

In $ \mathbb{R}^3$ , suppose there is a curve on X-Y plane $ y(x)$ defined on $ x\in [-a,a]$ satisfying:

  1. $ y(x)\geqslant 0$ ;
  2. $ y(-a)=y(a)=0.$

Rotate $ y(x)$ along x-axis in $ \mathbb{R}^3$ and get a solid revolution.

Minimize surface area $ A=\int_{-a}^{a}2\pi y\sqrt{1+(y’)^2}\mathrm{d}x$ , given fixed volume $ V=\int_{-a}^{a}\pi y^2\mathrm{d}x=C$ , for some constant $ C$ .

By standard variational method and Lagrange multiplier, ($ \lambda$ is Lagrange constant), we get the Euler Lagrange equation, which is nonlinear. $ $ \frac{1}{(1+(y’)^2)^{1/2}}+\lambda y = \frac{yy”}{(1+(y’)^2)^{3/2}}$ $

My question is how to do with this nonlinear equations. Is there any way to get the minimal $ A$ without solving $ y$ explicitly?

How to write unit tests a method with a result that is highly based on another method

How to write unit tests a method with a result that is highly based on another method ?

async function getStatus(   session,   correlationId,   data ) {    const client = new SomeAPIWrapperClient({     correlationId: correlationId,     timeout: 10000   })    const result = await client.createSession(data)    return result.status == 'SUCCESS';  } 

Should I test that the method is creating a new SomeAPIWrapperClient and passing the received correlationId and 10000 !

Should I check if the client.createSession is called once with the passed data

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