Class Note

Note

For making an API for server, here are a few necessary files: server.js: defines which port to listen to, and to express package.js: keep record of all packages/dependancies required for running the server.js Node.js is going to run these files and operate different responses for requests
Type html:5 in index.html, it will automatically put in the simple html code (at least for visual studio code)
127.0.0.1 is all computer’s “me”, meaning that that address indicates themselves. For two programs on the same computer talking to each other, they communicate through 127.0.0.1, with different port numbers that individual programs are listening to. </aside>

In a server node folder: NewProject

node_modules (this is created when “npm node”)
public (I need to create this mysel
- index.html
package-lock.jason
package.jason (automatically created when server.js is created)
server.js (I need to create this myself) </aside>

npm.init

The npm init command is used to initialize a new Node.js project and create a package.json file. This file stores metadata about your project, including its name, version, description, entry point, dependencies, and more.

</aside>

Assignment

VS Code can’t connect to remote host

I was trying to login to my droplet via VS Code, but encountered an error saying: "VS Code Could not establish connection to 'my droplet': Connecting with SSH timed out"

Trouble shoot 1: This might be happening because there’s corruption in VS Code’s configuration file in the remote host, I tried to use terminal to delete file: ~/.vscode-server. (This approach works at first, but after successfully login, VS Code showed “failed to reload” after a couple minutes)
Trouble shoot 2: The issue might be short in RAM, thus I use the below code for debug:

~$ sudo dmesg | grep -i kill

[5810308.157291] systemd-journal invoked oom-killer: gfp_mask=0x140cca(GFP_HIGHUSER_MOVABLE|__GFP_COMP), order=0, oom_score_adj=-250
[5810308.157342]  oom_kill_process.cold+0xb/0xaf
[5810308.157878] oom-kill:constraint=CONSTRAINT_NONE,nodemask=(null),cpuset=/,mems_allowed=0,global_oom,task_memcg=/user.slice/user-1000.slice/session-11602.scope,task=node,pid=1021040,uid=1000
[5810308.157928] Out of memory: Killed process 1021040 (node) total-vm:33316388kB, anon-rss:98124kB, file-rss:2876kB, shmem-rss:0kB, UID:1000 pgtables:3020kB oom_score_adj:0

The message showed Out of memory error.

I also checked my remaining flash memory:

~$ df -h /
Filesystem      Size  Used Avail Use% Mounted on
/dev/vda1        24G  5.2G   18G  23% /

I can swap some flash memory into RAM:

acan@understanding-networks-25-dev:~/NodeExamples/newProject$ free -h
               total        used        free      shared  buff/cache   available
Mem:           960Mi       940Mi        69Mi       6.7Mi        54Mi        20Mi
Swap:             0B          0B          0B
acan@understanding-networks-25-dev:~/NodeExamples/newProject$ sudo fallocate -l 2G /swapfile
acan@understanding-networks-25-dev:~/NodeExamples/newProject$ sudo chmod 600 /swapfile
acan@understanding-networks-25-dev:~/NodeExamples/newProject$ sudo mkswap /swapfile
Setting up swapspace version 1, size = 2 GiB (2147479552 bytes)
no label, UUID=3a4739fb-f41a-4a33-bf6e-10a11d3ebebe
acan@understanding-networks-25-dev:~/NodeExamples/newProject$ sudo swapon /swapfile
acan@understanding-networks-25-dev:~/NodeExamples/newProject$ free -h
               total        used        free      shared  buff/cache   available
Mem:           960Mi       897Mi        95Mi       6.7Mi        89Mi        63Mi
Swap:          2.0Gi        67Mi       1.9Gi

And this fixed my issue.

</aside>

<aside>

API up and running!

URI: https://www.rayrayrule.me

How the API works

https://www.rayrayrule.me/entropy/ —>shows a list of entropy value in different elements

https://www.rayrayrule.me/entropy/carbon —>filter out the specific elements

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