Knowledge base

knowledge-base.md

Knowledge base

All interesting links and reflections throughout time goes here.

Cheat Sheet

Postgres UUID

create extension "uuid-ossp";
select uuid_generate_v4();

Postgres UPDATE FROM SELECT

UPDATE
    Table_A
SET
    Table_A.col1 = Table_B.col1
FROM
    Some_Table AS Table_A
WHERE
    Table_A.col3 = 'cool'

Create new table from existing

alter table tablename rename to oldtable;
create table tablename (column defs go here);
insert into tablename (col1, col2, col3) select col2, col1, col3 from oldtable;
alter table tablename OWNER TO someownerifneeded;

Replace text on file using sed

sed -i '' 's/old/new/g' /path/to/file.txt

Git replace master with our branch

git checkout seotweaks
git merge -s ours master
git checkout master
git merge seotweaks

Git update submodules

git submodule foreach git pull origin master

Git update fork

git remote add upstream git://github.com/ORIGINAL-DEV-USERNAME/REPO-YOU-FORKED-FROM.git
git fetch upstream
git pull upstream master

Git copy code from VSTS to GitHub (or others)

git clone --mirror <url_of_old_repo>
cd <name_of_old_repo>
git remote add new-origin <url_of_new_repo>
git push new-origin --mirror
git remote rm new-origin

Kubernetes delete evicted pods

kubectl get pods | grep Evicted | awk '{print $1}' | xargs kubectl delete pod

Flux Sync

alias ff='fluxctl sync --k8s-fwd-ns flux'

Flux Helm Sync

kb exec -n flux helm-operator-5f85794486-xq59m -- curl -XPOST http://localhost:3030/api/v1/sync-git

Go dependencies graph

godepgraph -nostdlib -horizontal -onlyprefixes=github.com/repo/svc github.com/repo/svc/cmd/server | dot -Tpng -o godepgraphz.png

Links

General

• Understanding functor and monad
• Understanding OKR

C#

• Use class for identity and behaviour (DDD).
• Use struct for value objects without behaviour (such as Money).
• The record keyword adds IEquatable and ToString comparators.
• A record class is inmmutable, you can create copies with the with keyword.
• A record struct is mutable unless you add the readonly keyword.

Golang

• Slice of pointers
• Iterating over slices
• Slices and internals
• Collections of unknown length
• Slice append
• Altered slices by value
• Cap vs len
• Communicating Sequential Processing
• Sleep sort
• Guide to timeouts
• Context package
• Context cancellation
• Postgres in Go, prepared statements

Postgres

• Fetch first with ties
• Pgbouncer diagnostic info
• Prometheus exporter for Pgbouncer
• Pgbouncer and prepared statements
• Pgbouncer, Golang and prepared statements

Github Pages

• Add custom DNS

Kubernetes

• Pod disruption budget
• PVC created by statefulset not removed by design
• Understanding CPU and Memory with Vertical Pod Autoscaler
• Megabyte vs mebibyte
• Rightsize Your Pods with Vertical Pod Autoscaling
• Restart-Free Vertical Scaling for Kubernetes Pods
• Kubernetes best practices: Resource requests and limits
• Horizontal Pod Autoscaler Walkthrough

Kubernetes Summary

• Health check: Restarts pod if it does not work, so just check the internal dependencies, that can be solved with a restart, are up.
• Ready check: Stop routing traffic if it does not work, check external dependencies, now beware you can actually give cause latency issues or denial of service to yourself, be conservative.
• Cluster autoscaling: Feature of GKE, add more nodes workers to certain node pool.
• Horizontal scale: Upon certain metric (could be custom or could be cpu/mem) reaches a % another replica could be spawned.
• Vertical scale:
  • Has 2 modes, recommendation and update. Possibility of excluding certain container of a pod.
  • On recommendation it tells you how much mem/cpu you need to assign as resource.
  • On auto it kills the pod and spawns a new one with new resource.
  • Does not work on auto when only 1 replica.
  • Pdb is recommended so you don't have downtime.
• Goldilocks:
  • Tool that exposes dashboard and fires vpa for every container on namespace.
  • Dashboard allows you to port forward and check the recommended limits, so you change yourself.
• Resources:
  • Requests: The minimum the scheduler needs to allocate for running this container.
  • Limits: Pod can reach up to this amount, in an overcommited state (likely to be killed).
  • cpu: 50m is expressed in millicores, 1000 is 1 cpu, 250 1/4 cpu. In case of overcommitted it will get throttled.
  • memory: Expressed in Mi as memybytes. In case of overcommitted it will get killed.

Istio

• Cronjobs not ending because of Istio proxy
• Istio ports 31400 and 15443
• Istio on GKE private cluster, create firewall rule
• Injection diagnosis
• Migration init container running before proxy

BankID

• Test certificate for BankID
• Unofficial bankID lib
• BankID docs
• Formatted text for visible data
• Get test BankID on mobile and PC
• Issue a test bank ID with your real one

Signicat

• Get access token
• Preprod credentials
• Signing steps
• Log in to OIDC clients