Today I learnt

Today I learned how to copy aws EC2 amis between regions usin aws CLI. aws ec2 copy-image --name "{}" --source-image-id "{}" --source-region "{}" --region "{}" --name is for the name of the ami in the new region, and --region is for the destination region. I used it to migrate a bunch of amis from a region to another from subprocess import Popen, PIPE import json import mysql.connector def kebab(name): return name.lower().replace('_', '-').replace(' ', '-') mydb = mysql.connector.connect( host="localhost", user="user", passwd="password", database="database" ) c = mydb.cursor() c2 = mydb.cursor() c.execute("SELECT * FROM aws_images") results = c.fetchall() for i, result in enumerate(results): name = kebab(result[2]) if result[2] else "unnamed-{}".format(i) ami = result[8] try: cmd = 'aws ec2 copy-image --name "{}" --source-image-id "{}" --source-region "us-east-2" --region "eu-west-1"'.format(name, ami) stream = json.loads(Popen(cmd, shell=True, stdout=PIPE).stdout.read()) new_img = stream['ImageId'] cmd = 'UPDATE aws_images SET ami_id="{}" WHERE id={}'.format(new_img, result[0]) c2.execute(cmd) print("changed {} with {}\n{}".format(ami, new_img,'-'*15)) except Exception as e: print(e) continue mydb.commit()

Today I learned about DNS and how it works, and learned some terminology as well. First I followed this awesome playlist. Here is what I learned from it: Video 1: DNS Tree structure: DNS domains and hostnames are stored in a tree structure, with the root domain (.) at the top. Video 2: The hierarchy is composed of the root domain at the top, then top level domain (.com, .info, .us …) and fully qualified domain names (google.com, mail.google.com…). We got also domains, sub-domains and hosts which are real machines. BTW hostname != domain name there are domains that does not refer to real machines. Video 3: DNS zones are portion of the DNS space with a manager which we delegate queries to (Delegation) Video 4: DNS is a database containing information about names of ip addresses. DNS has nothing to do with geography, and IP routing (DNS is a tree). Video 5: How DNS queries work, going from a zone to another (delegated) until it reaches the wanted domain. Video 6: Client contacts the DNS server in the configuration (resolv.conf), who itself contacts other DNS servers (starting from a root server, containing a root zone) recursively until the DNS name is resolver. Then I fired up wireshark And tried to sniff some DNS packets and try to see what is inside them. ...

Today I learned about keychain and how to use it to manage ssh and gpg agents. Keychain create one ssh-agent per system, unlike ssh-agent that creates one agent per login session (if placed in zprofile) and require multiple ssh-add for keys. In addition to that ssh-agent is not compatible with cron jobs or shell scripts because they do not inherit the SSH_AUTH_SOCK variable from the environnement. # run a ssh agent and add the id_rsa key (using keychain) eval `keychain --eval --agents ssh id_rsa` Option Use –agents specify agents to run (gpg or ssh) –clear clear the cached keys for every new login -k [all|mine] kill all the agents, or only agents started by keychain –dir specify the dir where the SSH_AUTH_SOCK will be cached

Today I learned about git tags, and how to use them to control job triggering in gitlab ci. Git tags are ref’s that point to specific points in Git history. There are two types: Lightweight which act as bookmarks for specific commits (can be thought of as private) and Annotated which stores extra meta data like tagger’s name and email address. git tag <tagname> #lightweight git tag -a <tagname> -m <tag_message> #annotated To trigger jobs according to tags we either use only:/except: or job(or workflow) rules. ...

Today I learned how to get information about databases and tables in mysql. show databases; use <database-name> show tables; describe <table-name>;

AWS restricts traffic on port 25 of all EC2 instances by default, you should open a request to remove the restriction. More details here

Today I learned how to prevent tmux from starting a login shell set-option -g default-command zsh Here