minecraft-ondemand

Almost free serverless on-demand Minecraft server in AWS

Background

Instead of paying a minecraft hosting service for a private server for you and your friends, host it yourself. By utilizing several AWS services, a minecraft server can automatically start when you're ready to use it, and shut down when you are done. The final cost will depend on use but can be as little as a a dollar or two per month. The cost estimate breakdown is below.

This is a reasonably cost effective solution for someone that doesn't need their server running 24/7. If that's you, read on!

Workflow

The process works as follows:

1. Open Minecraft Multiplayer, let it look for our server, it will time out.
2. The DNS lookup query is logged in Route 53 on our public hosted zone.
3. CloudWatch forwards the query to a Lambda function.
4. The Lambda function modifies an existing ECS Fargate service to a desired task count of 1.
5. Fargate launches two containers, Minecraft and a watchdog, which updates the DNS record to the new IP
6. The watchdog optionally sends a text message through Twilio when the server is ready.
7. Refresh Minecraft server list, server is ready to connect.
8. After 10 minutes without a connection or 20 minutes after the last client disconnects (customizable) the watchdog sets the desired task count to zero and shuts down.

Diagram

Requirements

• AWS Account
• Domain name with public DNS served from Route 53. Does not need to be registered through Route 53.
• Minecraft Java edition client (though it could probably be tweaked to work with bedrock edition)
• Use of the excellent Minecraft Docker server image (used within task definition, no direct download required)

Cost Breakdown

• Link to AWS Estimate assuming 20 hours a month usage.
• tl;dr : $0.50 per month for DNS zones, $0.0149 (one point five cents) per hour for Fargate Spot or $0.049 (four point nine cents) per hour for regular Fargate. All other costs negligible, a couple of pennies per month at most.
• tl;dr;tl;dt : $1.50 / month for 20 hours of play.

Installation and Setup

One day, this could be a Cloud Deployment Kit script. Until then, these steps are required.

Region Selection

While it doesn't matter which region you decide to run your server in, Route 53 will only ship its logs to us-east-1, which in turns means that the lambda function also has to be in us-east-1. This lambda function can fire off the server in another region without issue, as long as the destination region is specified within the lambda function code. For the purposes of this documentation, I'm using us-west-2 to run my server.

Check the region in each ARN if you're copy/pasting. Remember that some stuff has to be in us-east-1 no matter what.

VPC

A VPC with Subnets must exist in order for Fargate tasks to launch and for EFS shares to be mounted. A subnet should exist in each availability zone so that Fargate (and Fargate Spot, if used) can properly launch the tasks in an AZ with plenty of capacity. A security group for our task is required but is easiest configured when setting up the Task Definition below.

A Default VPC should do the trick, chances are you've already got one.

Elastic File System

EFS is where the world data and server properties are stored, and persists between runs of the minecraft server. By using an "Access Point" the mounted folder is created automatically, so no mounting of the EFS to an external resource is required to get up and running. To make changes to the files like server.properties later however, a user can either mount the EFS file system to a Linux host in their account if they're comfortable with that, or I detail another method below using AWS DataSync and S3 that anyone can use without Linux experience.

Creating the EFS

Open the Elastic File System console and create a new file system. Believe it or not, all the defaults are fine here! It will create an EFS available in each subnet within your VPC.

Select your newly created filesystem, and tap the Access Points tab. Create a new access point using the following specifics:

• Details
  • Root directory path : /minecraft
• POSIX User
  • User ID : 1000
  • Group ID : 1000
• Root directory creation permissions (this is required, otherwise our container won't be able to create the folder to store its data the first time)
  • Owner user ID : 1000
  • Owner group IP : 1000
  • POSIX Permissions : 0755

Click Create access point and then view it within the console. Note the Access Point ARN of the access point and of the filesystem itself as you will need it for the IAM policy detailed below.

IAM Round 1

The IAM Console is where we configure the roles and policies required to give access to the Task running the Minecraft server and the Lambda Function used to start it.

Ultimately we'll need to create:

• Role for the ECS Fargate Task
• Role for the Lambda function (Lambda will create this for us and we'll add permissions to it)
• Policy to read/write the EFS mount attached to the Task role (EFS ARN required to create this Policy)
• Policy to turn our ECS service and tasks on and off, attached to both the Task role and the Lambda role. (ECS cluster and service name required to create this Policy)
• Policy to update a DNS record in Route 53, attached to the Task role. (Hosted Zone ID required to create this Policy)

Role Generation

In the IAM console, create a new role for the ECS Fargate Task.

Call it something useful, like ecs.task.minecraft-server. Three policies must be linked to this role, but we are only ready to create the first one now.

EFS Policy

The first policy we need to create will allow for read/write access to our new EFS Access Point. Call it efs.rw.minecraft-data. You'll actually need TWO ARNs, one from the filesystem itself and one from the access point, both of which are in the EFS console. The Condition block is optional but is there with Principle of least privilege in mind.

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Effect": "Allow",
            "Action": [
                "elasticfilesystem:ClientMount",
                "elasticfilesystem:ClientWrite",
                "elasticfilesystem:DescribeFileSystems"
            ],
            "Resource": "arn:aws:elasticfilesystem:us-west-2:xxxxxxxxxxxx:file-system/fs-xxxxxxxx",
            "Condition": {
                "StringEquals": {
                    "elasticfilesystem:AccessPointArn": "arn:aws:elasticfilesystem:us-west-2:xxxxxxxxxxxx:access-point/fsap-xxxxxxxxxxxxxxxxx"
                }
            }
        }
    ]
}

Elastic Container Service

Cluster

Create a new "Networking Only" Cluster. Call it minecraft. Don't create a dedicated VPC for this, use the default or same one you already created your EFS in. Enabling Container Insights is optional but recommended for troubleshooting later, especially if you expect a lot of people to potentially connect and you want to view CPU or Memory usage.

Task Definition

Create a new Task Definition called minecraft-server.

• Task Role: ecs.task.minecraft-server (or whatever you called it when creating it above)
• Network Mode: awsvpc (default)
• Requires compatibilities: fargate (default)
• Task Execution Role: ecsTaskExecutionRole (default)
• Task Memory: 2GB (good to start, increase later if needed)
• Task CPU: 1 vCPU (good to start, increase later if needed)

Skip containers temporarily and go down to Volumes. Add a volume, call it data, volume type EFS. Select the filesystem id created above, the access point id created above, enable Encryption in transit and click Add.

Scroll back up and add a container. Call it minecraft-server.

• Image: itzg/minecraft-server
• Port Mappings: 25565 TCP
• Essential: NOT Checked (task stops with the watchdog container)
• Environment Variables.
  • EULA : TRUE
  • Any additional stuff you want from Minecraft Docker Server Docs
• Mount Points: data mounted to /data

Add a second container. Call it minecraft-ecsfargate-watchdog. If using Twilio to alert you when the server is ready and when it turns off, all four twilio variables must be specified.

• Image: doctorray/minecraft-ecsfargate-watchdog (source for this container within this project if you want to build/host it yourself)
• Essential: YES checked
• Environmental Variables
  • CLUSTER : minecraft
  • SERVICE : minecraft-server
  • DNSZONE : Route 53 hosted zone ID, this is a 21 digit string you used in the policy above.
  • SERVERNAME : minecraft.yourdomainname.com
  • TWILIOFROM : +1XXXYYYZZZZ (optional, your twilio number)
  • TWILIOTO : +1XXXYYYZZZZ (optional, your cell phone to get a text on)
  • TWILIOAID : Twilio account ID (optional)
  • TWILIOAUTH : Twilio auth code (optional)
  • STARTUPMIN : Number of minutes to wait for a connection after starting before terminating (optional, default 10)
  • SHUTDOWNMIN : Number of minutes to wait after the last client disconnects before terminating (optional, default 20)

Create task.

Service

Within your minecraft cluster, create a new Service. Under Capacity Provider, you've got a choice. If you leave it default, your tasks will launch under the FARGATE strategy by default, which currently will run about 5 cents per hour. You can switch it to Custom, enable only FARGATE_SPOT, and pay 1.5 cents per hour. While this is cheaper, technically AWS can terminate your instance at any time if they need the capacity. The watchdog is designed to intercept this termination command and shut down safely, so it's fine to use Spot to save a few pennies, at the extremely low risk of game interruption.

Select your task definition and version created above. Platform version can be LATEST or 1.4.0. Call the service name minecraft-server to match the policies and lambda function. Number of tasks should be 0 (this will prevent it from running now before it is ready, and the other processes adjust it later on demand). Everything else on this page is fine as default. Hit Next.

Select your VPC, and select all of the subnets individually, which will maximize your success of running Fargate Spot tasks.

For Security Group, click edit. Let it create a new security group. Change the default HTTP rule to Custom TCP and change the port to 25565 from Anywhere, which will allow anyone to connect to the server once it is online (they have to know the name of course!) You could also restrict by known IP addresses but this is cumbersome to update regularly. Tap save.

Ensure that "Auto-assign public IP" is ENABLED (this is default). Tap Next, Next, and Create Service.

IAM Round 2

Now that we know the cluster name and service name, we can create the IAM Policy for ECS control, and attach it to the Role we created earlier.

ECS Policy

The Elastic Container Service task that launches the containers needs to be able to control itself, and understand which network interface is attached to it in order to properly update the DNS records, as well as turn itself off when it's not in use. Within this policy we give full access for ECS to control its own service and correspoinding tasks, and describe all network interfaces in EC2. Replace the xxxxxxxxxxxx below with the appriopriate account ID in your ARN.

Call this policy ecs.rw.minecraft-service.

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Effect": "Allow",
            "Action": [
                "ecs:*"
            ],
            "Resource": [
                "arn:aws:ecs:us-west-2:xxxxxxxxxxxx:service/minecraft/minecraft-server",
                "arn:aws:ecs:us-west-2:xxxxxxxxxxxx:task/minecraft/*"
            ]
        },
        {
            "Effect": "Allow",
            "Action": [
                "ec2:DescribeNetworkInterfaces"
            ],
            "Resource": [
                "*"
            ]
        }
    ]
}

Attach this policy to the ecs.task.minecraft-server role created earlier.

Lambda

A lambda function must exist that turns on your minecraft service. We do this with a simple python function that change the "Tasks Desired" count from zero to one when it is invoked.

Because we are relying on Route 53+CloudWatch to invoke the Lambda function, it must reside in the N. Virginia (us-east-1) region.

Create a new function using Author from scratch. I've used Python 3.9 but the latest version available should be fine. Call it something like minecraft-launcher. The other defaults are fine, it will create an IAM role we will modify afterward. We do not need to specify a VPC.

Once the function has been created and you're in the code editor, replace the contents of the default lambda_function.py with this:

import json
import boto3

def lambda_handler(event, context):

  ecs = boto3.client('ecs', region_name='us-west-2')
  response = ecs.describe_services(
    cluster='minecraft',
    services=[
      'minecraft-server',
    ]
  )

  desired = response["services"][0]["desiredCount"]

  if desired == 0:
    ecs.update_service(
      cluster='minecraft',
      service='minecraft-server',
      desiredCount=1
    )
    print("Updated desiredCount to 1")
  else:
    print("desiredCount already at 1")

This file is also in this repository in the lambda folder. Change the region on line 6, if needed, to the location of where your ECS Cluster is. Then, click the Deploy button. Finally, head over to the IAM console, locate the role that was created by this lambda function, and add the ecs.rw.minecraft-service policy we created above to it so that it will actually work.

Lambda can be very inexpensive when used sparingly. For example, this lambda function runs in about 1600ms when starting the container, and in about 500ms if the container is already online. This means, running at a 128MB memory allocation, it will cost $0.00000336 the first time the server is launched from an off state, and about $0.00000105 every time someone connects to an online server, because anyone connecting will have to perform a DNS lookup which will trigger your lambda function. If you and four friends played once a day for a month, it would come out to $0.0002583, which is 2.6% of a single penny.

Route 53

Ensure that a domain name you own is set up in Route 53. If you don't own one, consider registering one. You can use Route 53 for convenience or go to one of the big domain providers. Either way, ensure you've got your nameservers set to host out of Route 53 as it's required for the on-demand functionality.

Server DNS Record

Add an A record with a 30 second TTL with a unique name that you will use to connect to your minecraft server. Something like minecraft.yourdomainname.com, or more complex if desired, as every time anyone in the world performs a DNS lookup on this name, your Minecraft server will launch. The value of the record is irrelevant because it will be updated every time our container launches. Use 1.1.1.1 ot 192.168.1.1 for now if you can't think of anything.

Query Logging

The magic that allows the on-demand idea to work without any "always on" infrastructure comes in here, with Query logging. Every time someone looks up a DNS record for your domain, it will hit Route 53 as the authoritative DNS server. These queries can be logged and actions performed from them. From your hosted zone, click Configure query logging on the top right.

In Log group select Create log group and use the suggested name with your domain name in the string, /aws/Route 53/yourdomainname.com and click Create.

IAM Route 53 Policy

This policy gives permission to our ECS task to update the A record associated with our minecraft server. Retrieve the hosted zone identifier from Route 53 and place it in the Resource line within this policy. Call it route53.rw.yourdomainname.

Note: This will give your container access to change all records within the hosted zone, and this may not be desirable if you're using this domain for anything else outside of this purpose. If you'd like to increase security, you can create a subdomain of the main domain for this purpose. This is an advanced use case and the setup is described pretty well within Delegate Zone Setup.

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Effect": "Allow",
            "Action": [
                "Route 53:GetHostedZone",
                "Route 53:ChangeResourceRecordSets",
                "Route 53:ListResourceRecordSets"
            ],
            "Resource": "arn:aws:Route 53:::hostedzone/XXXXXXXXXXXXXXXXXXXXX"
        },
        {
            "Effect": "Allow",
            "Action": [
                "Route 53:ListHostedZones"
            ],
            "Resource": "*"
        }
    ]
}

Attach this policy to your ECS Task Role.

CloudWatch

The final step to link everything together is to configure CloudWatch to start your server when you try to connect to it.

Open the CloudWatch console and change to the us-east-1 region. Go to Logs -> Log groups -> and find the /aws/Route 53/yourdomainname.com Log group that we created in the Route 53 Query Log Configuration. Optionally, modify the retention period to delete the logs after a few days so they don't accumulate forever.

Go to the Subscription filters tab, click Create and then Create Lambda subscription filter.

In the Create Lambda subscription filter page, use the following values:

• Lambda Function : minecraft-launcher or whatever you called it.
• Log format : other
• Subscription filter pattern: minecraft.yourdomainname.com (or just simply minecraft -- this is what it's looking for to fire off the lambda)
• Subscription filter name: minecraft

Click Start streaming.

Usage and Customization

To use your new server, open Minecraft Multiplayer, add your new server, and join. It will fail at first but then everything comes online and you can join your new world! You may notice that you don't have many permissions or ability to customize a lot of things yet, so let's dig into how to edit the relevant files!

Option 1: Mount EFS Directly

This option is the easiest for folks that are comfortable in the Linux command line, so I'm not going to step-by-step it. But basically, launch an AWS Linux v2 AMI in EC2 with bare-minimum specs, log into it, mount the EFS Access Point, and use your favorite command line text editor to change around server.properties, the ops.json, whitelists, whatever, and then re-launch your server with the new configuration.

Option 2: DataSync and S3

Since EFS doesn't have a convenient way to access the files outside of mounting a share to something within the VPC, we can utilize AWS DataSync to copy files in and out to a more convenient location. These instructions will use S3 as there are countless S3 clients out there you can manage files, including the AWS Console itself.

Step 1: Create an S3 bucket

Open the S3 console and create a bucket. It must have a unique name (across ALL s3 buckets). yourdomainname-files works pretty well. Place it in the same region as your EFS share. I always like to enable Bucket Versioning, in case you need to reference old files or restore to a different version. Also enable Server Side Encryption (why isn't this on by default?).

Step 2: Create an EFS -> S3 DataSync Task

Open the DataSync console and click Create task.

For Source location options, select Create new location with these options:

• Location type : Amazon EFS file system
• Region : The region your EFS is in
• EFS File System : The file system you created earlier (this is the file system itself not the access point)
• Mount path : /minecraft or wherever your Access Point is pointed to

Click Next. For Destination location options select Create new location with these options:

• Location type : Amazon S3
• Region : The region your bucket was created in
• S3 bucket : The bucket you created earlier
• S3 storage class : Standard is fine, these are really small files.
• Folder : /minecraft
• IAM Role : Click Autogenerate and it will fill this in for you.

Click Next. For Task Name consider something like minecraft-efs-to-s3. For the rest of the options, use these:

• Task execution configuration : Use all defaults
• Data transfer configuration
  • Data to scan : Entire source location
  • Transfer mode : Transfer only data that has changed
  • Keep deleted files / Overwrite files : Keep enabled as default
  • Excludes : add three excludes:
    • *.jar (this prevents copying the minecraft server binary
    • /world (we definitely don't want to overwrite your world...)
    • /logs (we can go to cloudwatch to look at these anytime)
• Schedule : not scheduled, we'll run it on demand
• Task logging
  • Log level : Do not send logs to CloudWatch

Click Next and Create task.

Step 3: Create an S3 -> EFS DataSync Task

Open the DataSync console and click Create task.

For Source location options, select Choose an existing location with these options:

• Region : The region your S3 bucket is in
• Existing locations : The S3 location you created in the previous step

Click Next. For Destination location options select Choose an existing location with these options:

• Region : The region your EFS is in
• Existing locations: The EFS location you created in the previous step

Click Next. For Task Name consider something like minecraft-s3-to-efs. For the rest of the options, use these:

• Task execution configuration : Use all defaults
• Data transfer configuration
  • Data to scan : Entire source location
  • Transfer mode : Transfer only data that has changed
  • Keep deleted files / Overwrite files : Keep enabled as default
  • Excludes : None necessary this time around
• Schedule : not scheduled, we'll run it on demand
• Task logging
  • Log level : Do not send logs to CloudWatch

Click Next and Create task.

Usage and file editing

After you've launched the minecraft server successfully once, it will create files in EFS such as server.properties, ops.json, whitelist.json among others. From the DataSync console, you can launch the minecraft-efs-to-s3 task, which will copy these files from the EFS share to your S3 bucket. Then you can download these files from S3 (using the console or something like S3 Browser), edit them on your computer, then use the same client to upload the files back to S3. Afterward, open DataSync and launch the minecraft-s3-to-efs task to copy the updated files back to your EFS share. Then when you launch the server again, it will see and use the new files.

Best practice would be, any time you want to make a change to always copy the latest files from EFS to S3 first while your server is off before editing them and copying them back. Otherwise you may unintentionally regress some settings.

Testing and Troubleshooting

The easiest way to trigger your process is to perform a dns lookup, which you can simply do by trying to visit your server name in a web browser. It will fail (duh) but it will also trigger your server to start up.

Areas of concern, what to watch

CloudWatch

Are your DNS queries getting logged properly? Check in the log groups, hit refresh. Often takes up to 30 seconds for them to show up.

Lambda

Is your function running? We didn't design a "test" functionality for it but you could!

Elastic Container Service

Can you start your server manually by setting desired count to 1? Here's some possible jumping off points for issues:

Service won't launch task

Check the execution roles, and that they have the right permissions. Check the container names for typos. Check that you selected multiple subnets in the task definition, and that it's using the LATEST version.

Containers won't switch to RUNNING state

Check all of the above, but also ensure you're using an EFS Access Point with the specified auto-create permissions. The minecraft container will fail if it can't mount the data volume.

Can't connect to minecraft server

Refresh. Wait a minute, especially the first launch. Check ECS to see that the containers are in the RUNNING state. Open the running task, go to the logs tab, select minecraft and see if there are any errors on the logs. Did you make sure you opened the right port (25565 TCP) to the world in the task security group?? Security groups can be edited from both the VPC and the EC2 console.

Not getting text messages

Are your Twilio vars valid? Do you have sufficient funds on your Twilio account? Check the logs on the watchdog container for any curl errors.

Server starts randomly?

Remember, the server starts with a DNS query automatically. So, if you've got buddies you've shared the server with, it may start up if they open their multiplayer screen to play on a different server if yours is in the list! If this is an issue, it could probably be mitigated with a more advanced CloudWatch Subscription Filter that checks against the source IP address in addition to just the domain name, with it limiting to your ISP or location.

Other Stuff

Concerned about cost overruns?

Set up a Billing Alert! You can get an email if your bill exceeds a certain amount. Set it at $5 maybe?

Twilio setup / usage

Open a free account at Twilio, and load it up with $10 or so of credit. You can purchase a phone number here for a small monthly fee, and pay per use text messaging. Doing this will allow the container to send you a text message when the server is available for use.

Suggestions, comments, concerns?

Open an issue, fork the repo, send me a pull request or a message.