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It also makes it very easy to back up your application data by snapshotting the EBS volume. 5 | 6 | AWS makes it easy to add additional EBS volumes to an EC2 Instance in CloudFormation templates, 7 | but it's not obvious from the AWS CloudFormation docs how to map an EBS volume 8 | to a Linux mount point, like `/var/myapp`. 9 | 10 | In this article I'll show you how to add an EBS volume to an EC2 instance and 11 | automatically mount the EBS volume to a directory/mount point inside the instance. 12 | 13 | # Deploying the CloudFormation template 14 | 15 | The example CloudFormation template we'll be using is at 16 | [1Strategy/blog-add-ebs-volume](https://github.com/1Strategy/blog-add-ebs-volume). 17 | 18 | If you'd like to try it out, clone the git repo and run this AWS CLI command to deploy it: 19 | 20 | ``` 21 | aws cloudformation deploy --template-file ./lvm-volume.yaml --stack-name lvm-volume --parameter-overrides VpcIdParameter=vpc-abcd1234 InstanceSubnetIdParameter=subnet-abcd1234 SshKeyParameter=mysshkey 22 | ``` 23 | 24 | # How to add an EBS volume in CloudFormation 25 | 26 | EBS volumes are block storage devices, and adding a block device to an instance requires 27 | only a [few lines of code in CloudFormation](http://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-properties-ec2-blockdev-mapping.html). 28 | 29 | 30 | ```YAML 31 | EC2Instance: 32 | Type: AWS::EC2::Instance 33 | Properties: 34 | BlockDeviceMappings: 35 | # Create a separate volume 36 | - DeviceName: /dev/sdf 37 | Ebs: 38 | DeleteOnTermination: false 39 | VolumeSize: 10 40 | ``` 41 | 42 | #### AWS Block Device naming conventions 43 | 44 | In the example above, I've named the block device `/dev/sdf`. See [Device Naming on Linux instances](http://docs.aws.amazon.com/AWSEC2/latest/UserGuide/device_naming.html) for more details on 45 | naming conventions for Linux block devices. In short, you should use `sdf - sdp`. 46 | 47 | Note that the OS, e.g. Amazon Linux, will rename `/dev/sdf` to `/dev/xvdf` (Xen Virtual Device "F"). For an explanation, see [Device Name Considerations](http://docs.aws.amazon.com/AWSEC2/latest/UserGuide/device_naming.html#device-name-limits) in the AWS EC2 User Guide. 48 | 49 | #### EBS Volume Attached But Not Usable 50 | 51 | If you deploy your CloudFormation template with this block device mapping, the EBS 52 | volume will be attached to your EC2 instance, but you won't be able to use it until 53 | you create a file system on it and mount it to a directory, or mount point, e.g. 54 | `/var/myapp`. 55 | 56 | 57 | # How to mount a volume in Linux automatically 58 | 59 | You can, of course, SSH in to your instance after creation and run the commands to 60 | create and mount a file system by hand, but if you are already using CloudFormation 61 | you want it all automated. In my case, I wanted to mount the EBS volume under 62 | `/var/myapp` so my application could store its data on a separate volume which 63 | wouldn't disappear if the instance was terminated. 64 | 65 | 66 | #### Running File System Create and Mount commands 67 | 68 | The CloudFormation snippet below uses AWS [CloudFormation::Init](http://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-resource-init.html), combined with 69 | [`cfn-init`](http://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/cfn-init.html) in the `UserData` 70 | section to run the commands to create and mount the file system at boot. 71 | 72 | Note that the commands are run in alphabetical order by name, *not* in the order listed in 73 | the `commands` section. That is why I've prepended each command with a number, 74 | e.g. `1_pvcreate`, `2_vgcreate`, etc. 75 | 76 | #### LVM 77 | I'm using [LVM](https://wiki.archlinux.org/index.php/LVM), or Logical Volume Manager, 78 | to make it easier to resize logical disk volumes in the future if need be. 79 | 80 | The `AWS::CloudFormation::Init` commands below first create an LVM physical volume, then a volume group, then a 81 | logical volume. 82 | 83 | #### File System 84 | After that, we create an [ext4](https://en.wikipedia.org/wiki/Ext4) 85 | file system, make the `/var/myapp` directory, and add the mount point to the 86 | `/etc/fstab` file so it will be mounted every time the system boots. 87 | 88 | Finally, we run the `mount -a` command to mount the newly added logical volume 89 | to the `/var/myapp` directory. 90 | 91 | ```YAML 92 | EC2Instance: 93 | Type: AWS::EC2::Instance 94 | Metadata: 95 | AWS::CloudFormation::Init: 96 | config: 97 | commands: 98 | 1_pvcreate: 99 | command: pvcreate /dev/xvdf 100 | 2_vgcreate: 101 | command: vgcreate vg0 /dev/xvdf 102 | 3_lvcreate: 103 | command: lvcreate -l 100%FREE -n myapp vg0 104 | 4_mkfs: 105 | command: mkfs.ext4 /dev/vg0/myapp 106 | 5_mkdir: 107 | command: mkdir /var/myapp 108 | 6_fstab: 109 | command: echo "/dev/mapper/vg0-myapp /var/myapp ext4 defaults 0 2" >> /etc/fstab 110 | 7_mount: 111 | command: mount -a 112 | Properties: 113 | BlockDeviceMappings: 114 | 115 | UserData: 116 | Fn::Base64: !Sub | 117 | #!/usr/bin/env bash 118 | set -o errexit 119 | yum -y update aws-cfn-bootstrap 120 | /opt/aws/bin/cfn-init -v --stack ${AWS::StackName} --resource EC2Instance --region ${AWS::Region} 121 | /opt/aws/bin/cfn-signal --exit-code $? --stack ${AWS::StackName} --resource EC2Instance --region ${AWS::Region} 122 | 123 | ``` 124 | 125 | #### UserData -> cfn-init -> AWS::CloudFormation::Init 126 | 127 | In the snippet above, the `UserData` section is run once at OS first boot as a Bash script. 128 | It calls `cfn-init` which triggers the `AWS::CloudFormation::Init` section in the 129 | Metadata section above. This is the recommended pattern for running bootstrap commands on 130 | your Linux instance. See [AWS::CloudFormation::Init](http://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-resource-init.html) 131 | for more details. 132 | 133 | #### Note 134 | If you are installing an application package which will create directories under 135 | your `/var/myapp` mount point, be sure to run the commands to create the mount 136 | point before installing your package. Otherwise the sub-directories the package 137 | creates will be wiped out. 138 | 139 | # Results 140 | 141 | After running the complete CloudFormation template you will have the `/var/myapp` 142 | directory mounted on your `/dev/sdf` (or `/dev/xvdf`) EBS volume. If your instance 143 | disappears, your data will not be lost. You can spin up another EC2 instance and 144 | mount the orphaned volume to recover your data. Note that once you've created 145 | a file system and LVM volumes you won't need to create them again for that EBS 146 | volume. 147 | 148 | You can view information about your EBS volume and mount point by running the 149 | `lsblk` command on your instance. Run `man lsblk` for more info. 150 | 151 | ``` 152 | $ lsblk --fs /dev/sdf 153 | 154 | NAME FSTYPE LABEL UUID MOUNTPOINT 155 | xvdf LVM2_member jgzpM5-... 156 | └─vg0-myapp ext4 165452b3-... /var/myapp 157 | ``` 158 | 159 | # Summary 160 | 161 | The full example CloudFormation template is at 162 | [1Strategy/blog-add-ebs-volume](https://github.com/1Strategy/blog-add-ebs-volume). 163 | 164 | Creating a separate EBS volume can be very useful to prevent application data loss 165 | in the event your EC2 instance is unexpectedly terminated. It also makes it very 166 | easy to back up your application data by snapshotting the EBS volume. Finally, 167 | it cleanly separates your application data from your OS root volume. 168 | 169 | In this post, I showed you, via a AWS CloudFormation template, how to create an 170 | EC2 Instance with an EBS volume to store your application data separately from your 171 | EC2 instance's root volume. 172 | 173 | You also learned how to create an LVM volume and ext4 filesystem on your EBS volume, 174 | and how to auto-mount the file system at boot by adding a line to your `/etc/fstab` 175 | file. 176 | 177 | I hope this helps you improve your CloudFormation templates when dealing with EBS volumes for applications. 178 | -------------------------------------------------------------------------------- /lvm-volume.yaml: -------------------------------------------------------------------------------- 1 | --- 2 | AWSTemplateFormatVersion: 2010-09-09 3 | Description: > 4 | EC2 instance with additional EBS volume set up as an LVM volume. 5 | 6 | Copyright 2017 1Strategy 7 | 8 | Licensed under the Apache License, Version 2.0 (the "License"); 9 | you may not use this file except in compliance with the License. 10 | You may obtain a copy of the License at 11 | 12 | http://www.apache.org/licenses/LICENSE-2.0 13 | 14 | Unless required by applicable law or agreed to in writing, software 15 | distributed under the License is distributed on an "AS IS" BASIS, 16 | WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 17 | See the License for the specific language governing permissions and 18 | limitations under the License. 19 | 20 | Parameters: 21 | VpcIdParameter: 22 | Description: Launch EC2 instance in this VPC 23 | Type: AWS::EC2::VPC::Id 24 | InstanceSubnetIdParameter: 25 | Description: Launch EC2 instance in this subnet 26 | Type: AWS::EC2::Subnet::Id 27 | SshKeyParameter: 28 | Description: SSH Keypair to login to the instance 29 | Type: AWS::EC2::KeyPair::KeyName 30 | InstanceAMIParameter: 31 | Description: Launch EC2 instance from this AMI 32 | Type: AWS::EC2::Image::Id 33 | Default: ami-8ca83fec 34 | InstanceTypeParameter: 35 | Description: EC2 instance family/size, e.g. t2.large 36 | Type: String 37 | Default: t2.micro 38 | 39 | Resources: 40 | InstanceSecurityGroup: 41 | Type: AWS::EC2::SecurityGroup 42 | Properties: 43 | GroupDescription: Allow SSH from the Internet. 44 | VpcId: !Ref VpcIdParameter 45 | SecurityGroupIngress: 46 | - IpProtocol: tcp 47 | FromPort: '22' 48 | ToPort: '22' 49 | CidrIp: 0.0.0.0/0 50 | EC2Instance: 51 | Type: AWS::EC2::Instance 52 | Metadata: 53 | AWS::CloudFormation::Init: 54 | config: 55 | commands: 56 | 1_pvcreate: 57 | command: pvcreate /dev/xvdf 58 | 2_vgcreate: 59 | command: vgcreate vg0 /dev/xvdf 60 | 3_lvcreate: 61 | command: lvcreate -l 100%FREE -n myapp vg0 62 | 4_mkfs: 63 | command: mkfs.ext4 /dev/vg0/myapp 64 | 5_mkdir: 65 | command: mkdir /var/myapp 66 | 6_fstab: 67 | command: echo "/dev/mapper/vg0-myapp /var/myapp ext4 defaults 0 2" >> /etc/fstab 68 | 7_mount: 69 | command: mount -a 70 | Properties: 71 | BlockDeviceMappings: 72 | # Create a separate volume 73 | - DeviceName: /dev/sdf 74 | Ebs: 75 | DeleteOnTermination: false 76 | VolumeSize: 10 77 | ImageId: !Ref InstanceAMIParameter 78 | InstanceType: !Ref InstanceTypeParameter 79 | KeyName: !Ref SshKeyParameter 80 | SecurityGroupIds: 81 | - !Ref InstanceSecurityGroup 82 | SubnetId: !Ref InstanceSubnetIdParameter 83 | UserData: 84 | Fn::Base64: !Sub | 85 | #!/usr/bin/env bash 86 | set -o errexit 87 | yum -y update aws-cfn-bootstrap 88 | /opt/aws/bin/cfn-init -v --stack ${AWS::StackName} --resource EC2Instance --region ${AWS::Region} 89 | /opt/aws/bin/cfn-signal --exit-code $? --stack ${AWS::StackName} --resource EC2Instance --region ${AWS::Region} 90 | 91 | Outputs: 92 | EC2InstancePublicIp: 93 | Description: EC2 instance public IP address 94 | Value: !GetAtt EC2Instance.PublicIp 95 | --------------------------------------------------------------------------------