Flowchart of how slack decides to send a notification (Episode 3)

In this newsletter, we will talk about the following:

• Flowchart of how slack decides to send a notification

• Orchestration and choreography

• How to design secure web API access for your website?

• How does Amazon build and operate software?

Flowchart of how slack decides to send a notification

It is a great example of why a simple feature may take much longer to develop than many people think.

When we have a great design, users may not notice the complexity because it feels like the feature just working as intended.

What’s your takeaway from this diagram?

Image source: Slack Eng blog

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How do microservices collaborate and interact with each other?

There are two ways: orchestration and choreography

The diagram below illustrates the collaboration of microservices.

Choreography is like having a choreographer set all the rules. Then the dancers on stage (the microservices) interact according to them. Service choreography describes this exchange of messages and the rules by which the microservices interact.

Orchestration is different. The orchestrator acts as a center of authority. It is responsible for invoking and combining the services. It describes the interactions between all the participating services. It is just like a conductor leading the musicians in a musical symphony. The orchestration pattern also includes the transaction management among different services.

The benefits of orchestration:

1. Reliability - orchestration has built-in transaction management and error handling, while choreography is point-to-point communications and the fault tolerance scenarios are much more complicated.

2. Scalability - when adding a new service into orchestration, only the orchestrator needs to modify the interaction rules, while in choreography all the interacting services need to be modified.

Some limitations of orchestration:

1. Performance - all the services talk via a centralized orchestrator, so latency is higher than it is with choreography. Also, the throughput is bound to the capacity of the orchestrator.

2. Single point of failure - if the orchestrator goes down, no services can talk to each other. To mitigate this, the orchestrator must be highly available.

Real-world use case: Netflix Conductor is a microservice orchestrator and you can read more details on the orchestrator design.

Question - Have you used orchestrator products in production? What are their pros & cons?

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How to design secure web API access for your website?

When we open web API access to users, we need to make sure each API call is authenticated. This means the user must be who they claim to be.

In this post, we explore two common ways:

1. Token based authentication

2. HMAC (Hash-based Message Authentication Code) authentication

The diagram below illustrates how they work.

Token based

Step 1 - the user enters their password into the client, and the client sends the password to the Authentication Server.

Step 2 - the Authentication Server authenticates the credentials and generates a token with an expiry time.

Steps 3 and 4 - now the client can send requests to access server resources with the token in the HTTP header. This access is valid until the token expires.

HMAC based

This mechanism generates a Message Authentication Code (signature) by using a hash function (SHA256 or MD5).

Steps 1 and 2 - the server generates two keys, one is Public APP ID (public key) and the other one is API Key (private key).

Step 3 - we now generate a HMAC signature on the client side (hmac A). This signature is generated with a set of attributes listed in the diagram.

Step 4 - the client sends requests to access server resources with hmac A in the HTTP header.

Step 5 - the server receives the request which contains the request data and the authentication header. It extracts the necessary attributes from the request and uses the API key that’s stored on the server side to generate a signature (hmac B.)

Steps 6 and 7 - the server compares hmac A (generated on the client side) and hmac B (generated on the server side). If they are matched, the requested resource will be returned to the client.

Question - How does HMAC authentication ensure data integrity? Why do we include “request timestamp” in HMAC signature generation?

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How does Amazon build and operate software? 

In 2019, Amazon released The Amazon Builders' Library. It contains architecture-based articles that describe how Amazon architects, releases, and operates technology. 

As of today, it published 26 articles. It took me two weekends to go through all the articles. I’ve had great fun and learned a lot. Here are some of my favorites:

🔹Making retries safe with idempotent APIs

🔹Timeouts, retries, and backoff with jitter

🔹Beyond five 9s: Lessons from our highest available data planes

🔹Caching challenges and strategies

🔹Ensuring rollback safety during deployments

🔹Going faster with continuous delivery

🔹Challenges with distributed systems

🔹Amazon's approach to high-availability deployment