Mosaic

Slack had an outage at 4 January 2021 for about ~1 hour on their web application (they mentioned it as “tier” but I am assuming that it relates to their client-facing application). This Slack blog post discusses about how the problem was discovered (it also had a neat timeline diagram) and the cause of the problem. This is my takeaway of Slack’s start of year 2021 outage. Monitoring services should be made reliable. One major hinderance that Slack faced during the incident was the monitoring services were unable to be used. As a result, they reverted to manual ways (such as querying directly to their backends) to troubleshoot and recover the impacted systems. Balance between upscaling and downscaling of instances. The article does not go deep dive about this but it seems this scaling have a major part. It only mentioned about disabling downscaling and adding 1200 servers for the upscaling. Now, from what I know, these scalings are usually handled by the cloud provider. My best gu...

The complete article of the postmortem can to read here: Postmortem of database outage of January 31 . In summary, Gitlab.com has a database outage occurred that on 31 January 2017. This outage resulted in the lost of data spans over +6 hours. There are several takeaways that I learned from this postmortem. Setup several recovery mechanism that works in case the first choice cannot be relied . Gitlab have 3 ways of database backup: running scheduled pg_dump to S3, disk snapshots using Azure, and LVM snapshot that usually used to copy data from production to staging environment. The pg_dump cronjob failed because of a different version used for pg_dump (for PostgreSQL 9.2) and the database version (PostgreSQL 9.6). The Azure disk snapshot is used to only backup NFS server (I am guessing data for their application and others..?). Moreover, this is a disk recovery data which means if Gitlab needed to only restore database data. I imagine they should manually to choose which part of...

So, I know it is stated frequently that JavaScript is "a single-threaded" language. But it is non-blocking thanks to Web APIs. However, I was thinking whether it means that we can run something concurrently like in some other languages like Java, Go, or Python. I mean ES6 includes Promises and it was enhanced by async-await. So, is it possible to make use of Promises to run multiple things in the same time? It was fairly a simple experiment. All you need is A function that acts as a Promise (an async function), A method that will be run as a Promise and as a synchronous function, and A "container" function that holds both async function and plain function. With that three method in mind, this is the code that I came up with. function timelapse ( id ) { for ( let i = 1 ; i <= 1 _000_000; i++) { if (i % 500 _000 === 0 ) { console .log( ` ${ new Date ().getTime()} ${id} ` ); } } } async function asyncFunction ( id ) { ...

Rails has a lot of handy methods built-in that sometimes all you have to do is know it. In consequence, there are an overwhelming methods available to get specific time and/or date. This cheatsheet should provide some practical methods for Time, Date, DateTime that may help you in developing with Rails. I have also included an example output of each method so you don't have to manually enter it in rails console to know what the outcome would be. Here is a brief overview of what methods will be covered in this cheatsheet. Feel free to skip to the methods that you need or scroll around to know what methods there are. Maybe it will help you in the future. Enjoy! Current time and date ( now , current , today ) Specific day ( yesterday , tomorrow ) Specific moment in time ( beginning_of_minute , end_of_minute , beginning_of_hour , end_of_hour ) Specific time of the day ( beginning_of_day , middle_of_day , end_of...

In SQL, there is two clause used for filtering: WHERE and HAVING . Most of the time WHERE clause is sufficient. However, the reason why HAVING clause exist is because WHERE clause cannot filter aggregates. To show an example of how each clause can be used, let's say we are running an ice cream company. We produce several flavours of ice cream. We sell these ice creams to stores in multiple countries. Each store would have different stocks of our ice cream varieties. Our users are from all over the world. From that example, we have the following schema of the database. In the following section, I will show some examples for both clauses in PostgreSQL . I have created the database dump  so you can experiment with it yourself. WHERE clause We can use the WHERE clause to search stores that is available in a county with the following query. SELECT * FROM stores WHERE country = 'ID'; We can also use it to find users who cannot access o...