Amazon EC2, Nodejs, Tmux quick reference

Just a quick post so I remember what I did and how to do it again:

Set up an AWS EC2 instance:

Sign up for / log in to Amazon Web Services. When you get to the main screen full of icons, select EC2 (stands for Elastic Cloud Computing — elastic because its easily expandable). Then click through many screens. This time we selected an Ubuntu 12.something 64-bit instance, and we chose the smallest (free-est) stuff possible; I believe it was called a micro instance or something. When you have to set up ports and such, the two important ones (if you’re planning on setting up some testing web host, for example), are ssh and http. Both are of type TCP, and it’s okay to let them accept all IPs for now. Next up, I think you have to set up your ssh key. Amazon will create one especially for you. Download it and put it in a safe place. Don’t lose that key or you’ll have to redo everything from scratch. Okay, now that you’ve got your ssh key, keep clicking okay/launch until you get to a screen that shows what might be a list of running instances (at this point I/you only have one going). If you scroll to the right, you’ll see the Public DNS and Public IP for this running instance. You should also see a green circle under instance status that says it’s running. Excellent! Perhaps copy that Public IP address, for we’ll need it to ssh into our server.

Log into your shiny new instance:

Great! Now let’s ssh in. To do so, first you’ll need to change the permissions on your ssh key file to make it more exclusive.

Aside on File Permissions:

File permissions are a cool relic of cleverly storing large(ish) amounts of data in small ways. Permissions are made of three digit numbers which represent the User’s permissions in the left-most digit, the Group permissions in the middle digit, and the Others permissions (world? I dunno) are represented by the right-most digit. The file permissions for each user/group/whatever are represented (each digit) by adding up the permissions you are granting (0 – nuthin’, 1 – execute, 2 – write, 4 – read), so read-write-execute (rwx) is 7 (4 + 2 + 1), while read-write (rw) is 6 (4 + 2), and so on. For our purposes, we (the main user) would like to be able to read, write and execute our ssh key (honestly, all we need to be able to do is read it, but this is fine too), and we DON’T want others to have any permissions on it, so we’ll set our permissions to 700 (7 for us, 0 for group, 0 for everyone else). To do so, we go to the directory that we stored our ssh key in and type “chmod 700 filename” where filename likely ends in pem and is the name of our ssh key file. Done.

… back to logging in to our EC2 instance

Now that our permissions are more exclusive, let’s ssh in: “ssh -i ./path/to/sshkeyfile ubuntu@ipaddress” where ubuntu happens to be our default username since we have an ubuntu instance and ipaddress is the public ip address listed in that table in the EC2 Management Console that we were in two paragraphs ago. If all goes according to plan, you should see your new shell prompt: ubuntu@ip-###-##-##-###:~$. Now you can install whatever you need to feel happy using apt-get:


Type “apt-get update” to update your default package manager (apt-get). [NOTE: you will likely need to sudo the apt-get commands.] First up, I installed git: “sudo apt-get install git”. Next up, I installed nodejs: “sudo apt-get install nodejs” and npm: “sudo apt-get install npm”. You get the idea. Now you should be able to “git clone” and fetch yourself your project files. In order to run a server (such as node), you’ll likely have set up environmental variables (perhaps I’ll write a post on this someday soon, as I have recent mildly-hellish-but-ultimately-successful experience setting up env vars on heroku). To set environmental variables in bash you could either type them all out (“a=1”; “echo $a” => 1 to confirm) then run your server, OR you could write a bash script that you call. Here’s how I did that:

lil’ bash script to set environmental vars:

Your ubuntu instance comes with vim, so you can type “touch .env” to make the file, then “vim .env” to open it for editing.

Very quick Vim intro aside:

Vim in short: it has modes. Press “i” to begin editing (now you’re in INSERT mode, as you’ll see at the bottom), or the escape key to go back to COMMAND mode. Typing “:wq” in command mode will save your file and quit out of vim. That’s all that’s necessary here.

… back to a bash env script:

Now that you have your .env file open in vim for editing, type commands as you would in bash. You’ll likely want to set things like “PORT=80” and on a newline “CLIENT_SECRET=yourcrazyapistring”, etc. Once you’ve typed in those important things that your app will need to know to run, save and get out of vim (esc, “:wq”). Now, run your .env file by typing “source .env”. [NOTE: you can also run it with “bash .env” but that will run it inside a tiny bash instance that will run the given script then exit, without keeping what you’ve set as fact in the current instance of your bash shell, which is why we’re instead using the source command.] Grrreat! Now you can run your server (in my case, cd to the folder my app is in and type “node app.js”).

On tmux

Okay, so far, so good, but what happens when we control-C and log out of our ubuntu server? It powers down! Or rather, once we log out of our bash session, whatever web server we’ve started in there will stop. So. We need a way to trick it into staying open even if we are not logged in: enter tmux. Tmux will let us begin a session and detach from it, letting it run by itself. [NOTE: at this point, if we’re really going to run a real website, we would do a lot of other things instead, such as install and use nginx, but that’s for another day.] So, how do we use tmux? First up, install it “sudo apt-get install tmux”. Then run it: “tmux”, which gives us a cute little bash-within-a-bash from which we can do normal things. (To get out: type “exit”). Within tmux, use the command initiator key combo (control-b) to do things. For example, type control-b then “?” for the help. The cool part of tmux is that you can now detach from a session you have going by typing control-b then “d”. Now you have a detached session within which you could have your app server running. Try logging out of your ubuntu instance (control-c) and back in (ssh command in bold above) and then type “tmux attach” and you should be back into your detached session! How cool is that?!? (very cool). I think you can also name sessions and do a bunch of fancy stuff with tmux that I don’t know about. I did, however, find out how to list your active sessions (“tmux ls”) and kill them one-by-one (“tmux kill-session -t sessionnumber”) where sessionnumber is the number of the session listed when you type “tmux ls”. BAM!

SCP – Secure CoPy

Alright, one last tidbit: how to get files onto your new ec2 instance. Tricky. It seems that within terminal you are either looking at your own local machine or you are ssh’ed into another machine. Thankfully, there’s a secret bridge between the two: scp, which stands for secure copy. Here’s how it works: within terminal, in bash on your local machine, type “scp -i ./path/to/your/sshfile.pem ./path/to/file/youwanttocopy/onlocalmachine ubuntu@##.###.###.##:/home/ubuntu”. Let’s explain: “scp -i” means tell secure copy to use your identity file (your sshkey); “./path/to/your/sshfile.pem” the path to your ssh file on your local machine so that scp can connect securely to the remote computer; “./path/to/file/youwanttocopy/onlocalmachine” the path to the file (on your local machine) that you’d like to copy to the remote machine; “ubuntu@##.###.###.##:/home/ubuntu” remote username (default in my case is ubuntu) AT remote ip address, colon, existing file path on remote machine.

Okay, I think that’s all I learned from 9am – 10am today. Amazing!

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