Wij concluded our Introduction to Minecloud having determined to pauze the project into two parts: 1) an on-demand, ephemeral Minecraft server, and, Two) a web application to embark and zekering the server.
Today, I’m going to discuss the very first part&mdash,the server. (Code can be found here.)
Where to Host?
Since Amazon Web Services has bot the leading pioneer ter the cloud computing strijdperk, they were the demonstrable choice for hosting the server. I’m sure there are slew of other worthy vendors, but hey, if it’s good enough for Netflix, Dropbox, etc., then it’s good enough for mij.
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Te order to run a server on Amazon’s EC2 service, you actually launch a type of imaginario machine that they call an Amazon Machine Picture (AMI). You have a ton of plasticity on the type of imaginario machine that you can run. If you want to run Linux, you can run any flavor you choose. If Windows is your thing, you can do that, too.
One strategy for EC2 users is to launch an AMI with a stock install of their preferred operating system, and then install and configure software after they launch it. Obviously, this adds time until a server is ready to use. However, if you’re running the same type of server overheen and overheen, it makes more sense to use a customized AMI that is already pre-configured with your choice of software, so that it is ready to go spil soon spil it is launched. You can choose from AMIs built by others that are available te their AMI Marketplace, or you can create your own custom-made AMI.
Not remarkably, a search for Minecraft ter the Marketplace turned up nothing, so I had to create my own.
What Needs to Run?
What do I need to install to get a fully operational Minecraft server that can be launched by the Minecloud web application? I began with an Ubunutu 12.04 cojín pic and added the following chunks:
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Java. Rather than use open JDK, I determined to use the Oracle JDK, even tho’ it is more of a agony to install. I couldn’t find a definitive recommendation for sticking with the Oracle JDK (the Minecraft Wiki pagina is spil close to definitive spil I could find), but I’ve seen reports of better stability using it, and I take convenience ter using the same version of Java that the Minecraft developers do.
Minecraft Server Manager (MSM). This is an awesome management script for Minecraft. It began it’s life spil an init script to commence the Minecraft server automatically during bootup, but then grew to be so much more, treating tasks like backups and Minecraft updates.
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Minecloud Management Scripts. While MSM can back up Minecraft worlds, it didn’t implement everything I needed to back up and restore the spel gegevens from an ephemeral server. Plus, I needed to manage who has permission to play on the server and track when players login and logout. For all thesis management tasks, I wrote several custom-made python and shell scripts.
Last requirement: All of the above had to be installed and configured to run automatically upon startup.
How to Build?
How do you create a custom-made AMI? The brief response is you take a snapshot of an already running EC2 example, and that becomes your fresh, bootable AMI. That means that our AMI creation process consists of three main tasks: launch an Ubuntu 12.04 server, install and configure software, and then take a snapshot. Wij could do the installation and configuration by mitt, but since this is a process that wij’ll need to do on a fairly regular ondergrond (to keep up with both Ubuntu updates spil well spil Minecloud updates), it’s best to automate it.
The implement I chose for automation is Puppet. There are slew of other configuration management options (chef, salt, ansible, to name but a few), but the official Learning Puppet Tutorial for beginners is fantastic, so I went with that. To use Puppet, you write “manifests” ter a custom-made domain-specific language that defines the state you want the server to attain. You can install packages, switch configuration files, commence and zekering services, and so much more.
While the Puppet manifests I wrote for Minecloud may not be downright idiomatic (I’m still a Puppet beginner, after all!), I loved having a accomplish set of instructions for building a server to my precies specifications ter a reproducible way. Super useful.
Of course, Puppet doesn’t treat the launching of an EC2 example, strafgevangenis the snapshotting and termination of it, so to that end, I included a build-ami.py script that treats all the steps necessary to create a custom-built Minecloud AMI. It launches an Ubuntu 12.04 example, uploads the Puppet manifests, applies the manifests, takes the snapshot, and ultimately shuts down the example.
It’s designed to be finta plain to use, but unluckily, it requires Python, Boto, and Fabric to be installed (preferably ter a virtualenv) on your particular machine, which can be a bit daunting for a non-Python developer. A better option that should be ready ter the near future is Mitchell Hashimoto’s latest project, called Packer, which is designed to create AMIs (and pictures for other platforms), but does it with a single binary, which is much simpler to install than a accomplish Python imaginario environment. Packer doesn’t have a Puppet provisioner just yet, but it’s coming soon, and merienda it does, I project to switch from my build-ami.py script to a solution based on Packer.
The Lifecycle of a Minecloud Server
Now that wij’ve gone through the process of building an AMI, what happens when you run it? Let’s examine all the tasks that a Minecloud server performs from bootup to shutdown.
Right after launch, the Minecloud server completes a number of tasks before it is ready to accept Minecraft players. (The names of the init scripts are ter parentheses.)
- Sync the spel gegevens files from S3. (msm-s3-sync)
- Update the Minecraft server to the latest version. (msm-jar-update)
- Update the list of players permitted to play ter the Minecraft world. (msm-update-auth-lists)
- Begin Minecraft spel. (msm)
- Notify the web application that Minecraft is ready. (msm-update-instance-state)
Merienda the bootup process completes and Minecraft is up and running, the following ongoing maintenance tasks are run spil cron jobs. (Names of cron jobs te parentheses.)
- Sync the spel gegevens files to S3. (msm-backup-working-files-to-s3)
- Notify the web application if any players loom ter or loom out. (msm-track-active-players)
Shutdown is the simplest of all.
- Zekering Minecraft spel. (msm)
- Perform a accomplish backup of all spel gegevens files to S3. (msm-pre-shutdown-backup.sh)
While that’s a pretty good overview of how the Minecloud server works, it’s possible that it’s not finta detailed enough for some. Well, if that describes your thinking, you’re ter luck! After all, I’ve got a reputation for exhaustive blog posts to maintain–so, lets dive into some of the details of the implementation.
Setting Environment Variables. Always
When a Minecloud EC2 example is running, it needs access to at least Trio chunks of configuration gegevens: the AWS_ACCESS_KEY_ID, the AWS_SECRET_ACCESS_KEY, and the name of the S3 bucket. While it’s possible to hard code thesis values into AMI during the AMI creation phase, that didn’t seem like the most nimble solution. Instead, following the lead of both the Twelve Autor App methodology and Heroku’s extensive use of configuration variables, I determined that all scripts on the Minecloud EC2 example would read their configuration from the environment.
Merienda I made that decision, the next step wasgoed to figure out how to do it.
Some googling showcased that there wasgoed a loterijlot of disagreement on how to best set environment variables on a system-wide ondergrond ter Linux so that they were available for all users. Some recommended editing /etc/profile , while others suggested /etc/bash.bashrc . Crimson Hat-based distributions favored adding custom-built .sh scripts under /etc/profile.d . But, for Ubuntu systems, the approved solution shows up to be to add them to an /etc/environment verkeersopstopping.
This worked superb. except for init.d scripts.
Many of the scripts that I run spil part of the booting up process rely on the variables I set ter /etc/environment , but unluckily, I discovered that the init.d process runs with a very restricted environment and doesn’t source that opstopping. Only the LANG and TERM variables are present ter the init environment.
For that reason, you’ll see this little snippet ter my init scripts that require access to /etc/environment variables:
I wasgoed anticipating having to do a similar workaround for cron jobs, since I came across many prayers for help ter setting environment variables for cron, but ter Ubuntu, it wasgoed a non-event, since “cron supports the pam_env module, and geysers the environment specified by /etc/environment.”
Don’t Dilly-Dally During Shutdown
Using init scripts to treat all the boot up tasks keeps things ordinary. To commence playing, you boot up a server and it automatically runs all the init.d scripts to set everything up and then notifies you when it’s ready to play.
Originally, I thought that shutting down could be treated the same way. Since I download the Minecraft spel gegevens files from S3 by running an init.d script during boot up, I figured I could upload those files back to S3 from the same init.d script during shutdown. And, it turns out I could. spil long spil it didn’t take too long.
Merienda I commenced testing the shutdown process with realistic spel gegevens, I kept experiencing truncated gegevens and incomplete backups on S3. Which wasgoed weird, since I never spotted that when I wasgoed running my little test world. After scraping my head about this for awhile, I posted a question on Stack Overflow, and AWS guru Eric Hammond helped set mij straight that it wasgoed the size of the gegevens I wasgoed backing up that wasgoed causing the problem, because I wasgoed prolonging the shutdown process beyond what Amazon permits.
Here’s an extract from his helpful response:
When you zekering or terminate an EC2 example, Amazon sends a soft shutdown request to the operating system to let it wrap up te a clean, safe manner. If the system does not indicate it is powering down within a brief time (minutes) then Amazon effectively pulls the power buttplug forcing a hard shutdown.
Backups are Pretty Significant
This entire idea of using makeshift servers falls exclusief if you can’t maintain the spel world ter a consistent state. That means that you need to back up the spel gegevens files when one server shuts down, and restore the spel gegevens files when the next server starts up. The go-to solution for very reliable, voortdurend storage is Amazon’s Elementary Storage Service (S3), so that’s where I determined to store all spel gegevens files and backups.
What to Back Up
Here’s the verkeersopstopping hierarchy for the Minecraft gegevens files:
To preserve the precies state of the Minecraft server, wij need to save everything under /opt/msm/servers/default , and conveniently enough, MSM has a instruction to zip up that directory:
Ideally, wij would like to back up the directory frequently, say every hour, so that if the server should crash, then at most you would lose 1 hour of spel play. The problem is, if wij save the MSM backup .zip verkeersopstopping every hour, then wij’re going to consume a loterijlot of storage space. For example, my backup .zip verkeersopstopping is overheen 300 MB ter size.
That suggests a hybrid backup strategy. Very first, save the directory spil individual files to S3 merienda an hour, overwriting the last files from the previous hour. Since many of the files won’t switch, it should be more efficient to perform an rsync-like backup, rather than save the .zip verkeersopstopping. Wij’ll call thesis backed up files the “working files.” 2nd, save the backup .zip opstopping at the end of a playing session right before the server shuts down. Thesis are called “archives,” and are only used if there should everzwijn be a problem with the working files and wij need to roll back to a previous point ter time.
How to Back Up
Spil I mentioned previousely, the Boto python library is fabulous for interacting with the AWS API. But, for reading and writing files to S3, it isn’t necessary to work directly with the low-level functionality that boto provides. Instead, there are slew of higher-level scripts that have already bot written to provide this functionality, and I evaluated three different ones to see which suited my needs the best:
s3put This script is included ter the boto package, and it provides a ordinary interface for writing files to S3. However, it doesn’t provide the capability to download files from S3.
boto-rsync This script is built on the boto library also, and what’s fine about boto-rsync is that not only can this script read and write to S3, it also partially emulates the behavior of rsync. Why only partially? Because, like rsync, it will consider a source verkeersopstopping and a destination opstopping to differ if they are different sizes. However, unline rsync, it won’t check to see if they have the same MD5 checksums, which means that if the source and destination files are different, but have the same opstopping size, then boto-rsync won’t recognize them spil different.
s3cmd Ter many ways, this is the best option of all. It can read and write to S3. And, it can better perform rsync style backups, since it verifies MD5 checksums. Unluckily, it isn’t based on Boto, so it has it’s own unique configuration.
Given its comprehensiveness, s3cmd certainly seemed like the best choice, but I went ter another direction, When I began working on the Minecloud project, s3cmd hadn’t bot updated ter a long time and I worried that the project wasgoed dying a slow death. More minor nits: I knew that I might be interested te using IAM roles for AWS permissions ter the future, which Boto supported, but s3cmd didn’t. And, I wasgoed annoyed by having to maintain two different configuration files for storing my AWS credentials.
For those reasons, I determined to use a combination of s3put (for writing to S3) and boto-rsync (for reading from S3) ter my backup scripts. However, development has picked up again on s3cmd, and merienda the fresh 1.Five version is officially released on PyPi, I most likely will switch overheen to it.
How to Back Up te the Future
The vormgeving of my backup project assumes that the single source of truth for Minecraft spel gegevens is the gegevens stored on S3, and what exists on the example filesystem is makeshift and can be thrown away with impunity. However, I now realize that Elastic Block Storage (EBS) volumes also provide voortdurend storage, and they may form the ondergrond for a better solution ter the future.
An EBS volume is block level storage that can be fastened to an EC2 example. That means I can store the /opt/msm filesystem to an EBS volume and link it to an EC2 example when I’m running it, and then detach it when I shut down the Minecraft EC2 example. What’s fine (and what I didn’t fairly grab spil I began working on this project) is that while it is detached, you only pay S3 storage charges for the volume (cheap!).
Thus, rather than copying working files to S3, I could just store them on the EBS volume, and only use S3 for the backed up archives. While it’s true that the reliability of EBS volumes isn’t spil good spil S3 (be sure to read their discussion of EBS Volume Durability) , it is still pretty darn fine. and I always have the backups available on S3 te case an EBS volume should fail.
What would this solve? Two things:
Much quicker launch and termination times. Copying a large Minecraft world (>500 MB) to S3 takes several minutes, but if wij link an EBS volume instead, wij can get rid of that waiting time altogether.
Simpler syncing of spel gegevens to voortdurend storage. Copying to disk is simpler than copying to S3.
That covers the basics of how the Minecloud AMI works. Coming soon te Part Trio: an overview of the Minecloud web application.