Block Storage

Block Storage offered by EGI Cloud providers

What is it?

Block storage provides block-level storage volumes for use within virtual machines (VMs). Block storage volumes are raw, unformatted block devices, which can be mounted as devices in VMs.

Block storage volumes that are attached to a VM are exposed as storage volumes that persist independently from the life of the VM, and need to be explicitly destroyed when data is not needed anymore. Users can create a file system on top of these volumes, or use them in any way you would use a block device (such as a hard drive).

The content of block storage volumes can be accessed only from within the VM they are mounted to, and they can be mounted to a single VM at any given time.

The main features of block storage:

Block storage is recommended for data that must be quickly accessible and requires long-term persistence.
Block storage volumes are well suited to both database-style applications that rely on random reads and writes, and to throughput-intensive applications that perform long, continuous reads and writes.
Users can create point-in-time snapshots of block storage volumes, which protect data for long-term durability, and they can be used as the starting point for new block storage volumes.

Note

Block storage volumes can only be mounted to VMs running at the same provider where the block storage is located.

Note

Block storage usage is accounted for the entire block storage device, regardless how much of it is actually used.

Important

There is a limit on the number of block storage devices you can attach on a VM and there is a limit to the maximum size of such virtual disks. These values will depend on the particular provider and your SLA.

Manage volumes

The block storage in the EGI Cloud is offered via OpenStack deployments that implement the Cinder service.

Users can manage block storage using the OpenStack Horizon dashboard of a provider, from a command-line interface (CLI), or via the OpenStack Block Storage API.

Manage from the command-line

Multiple command-line interfaces (CLIs) are available to manage block storage:

The OpenStack CLI
The FedCloud Client is a high-level CLI for interaction with the EGI Federated Cloud (recommended)
The Cinder CLI has some advanced features and administrative commands that are not available through the OpenStack CLI

The main FedCloud commands for managing volumes are detailed below.

Note

For more information see the documentation about volume management.

List volumes

For example, to list the volumes in the site IN2P3-IRES via the Pilot VO (vo.access.egi.eu), use the following FedCloud command:

To avoid passing the site, VO, etc. each time, you can use FedCloud CLI environment variables to set them once and reuse them with each command invocation.

$ export EGI_SITE=IN2P3-IRES
$ export EGI_VO=vo.access.egi.eu
$ fedcloud openstack volume list --site $EGI_SITE
Site: IN2P3-IRES, VO: vo.access.egi.eu, command: volume list
+---------------------------+--------+-----------+------+--------------------------------+
| ID                        | Name   | Status    | Size | Attached to                    |
+---------------------------+--------+-----------+------+--------------------------------+
| aa711296-5cff-46ac-bbe... | Matlab | in-use    |   50 | Attached to Moodle on /dev/vdb |
| b0abc762-a503-129d-3c1... |        | available |   30 |                                |
+---------------------------+--------+-----------+------+--------------------------------+

To avoid passing the site, VO, etc. each time, you can use FedCloud CLI environment variables to set them once and reuse them with each command invocation.

> set EGI_SITE=IN2P3-IRES
> set EGI_VO=vo.access.egi.eu
> fedcloud openstack volume list --site %EGI_SITE%
Site: IN2P3-IRES, VO: vo.access.egi.eu, command: volume list
+---------------------------+--------+-----------+------+--------------------------------+
| ID                        | Name   | Status    | Size | Attached to                    |
+---------------------------+--------+-----------+------+--------------------------------+
| aa711296-5cff-46ac-bbe... | Matlab | in-use    |   50 | Attached to Moodle on /dev/vdb |
| b0abc762-a503-129d-3c1... |        | available |   30 |                                |
+---------------------------+--------+-----------+------+--------------------------------+

To avoid passing the site, VO, etc. each time, you can use FedCloud CLI environment variables to set them once and reuse them with each command invocation.

> $Env:EGI_SITE="IN2P3-IRES"
> $Env:EGI_VO="vo.access.egi.eu"
> fedcloud openstack volume list --site $Env:EGI_SITE
Site: IN2P3-IRES, VO: vo.access.egi.eu, command: volume list
+---------------------------+--------+-----------+------+--------------------------------+
| ID                        | Name   | Status    | Size | Attached to                    |
+---------------------------+--------+-----------+------+--------------------------------+
| aa711296-5cff-46ac-bbe... | Matlab | in-use    |   50 | Attached to Moodle on /dev/vdb |
| b0abc762-a503-129d-3c1... |        | available |   30 |                                |
+---------------------------+--------+-----------+------+--------------------------------+

Create volume

To create a new volume use the FedCloud command below:

$ fedcloud openstack volume create --size 10 my-volume
Site: IN2P3-IRES, VO: vo.access.egi.eu, command: volume create --size 10 my-volume
+---------------------+------------------------------------------------------------------+
| Field               | Value                                                            |
+---------------------+------------------------------------------------------------------+
| attachments         | []                                                               |
| availability_zone   | nova                                                             |
| bootable            | false                                                            |
| consistencygroup_id | None                                                             |
| created_at          | 2021-08-05T13:10:42.000000                                       |
| description         | None                                                             |
| encrypted           | False                                                            |
| id                  | a711296-5cff-46ac-bbe3-58e00712ee3e                              |
| multiattach         | False                                                            |
| name                | my-volume                                                        |
| properties          |                                                                  |
| replication_status  | None                                                             |
| size                | 10                                                               |
| snapshot_id         | None                                                             |
| source_volid        | None                                                             |
| status              | creating                                                         |
| type                | ceph                                                             |
| updated_at          | None                                                             |
| user_id             | 1a3ef4b64714f86ac71f1c9512345678c157a94ae1b37f167b6a663baa3b915b |
+---------------------+------------------------------------------------------------------+

The status of the new volume will probably be returned as creating. To check if the volume finished creating, look at the details of the volume, or list only the newly created volume (filter by volume name or ID):

$ fedcloud openstack volume list --name my-volume
Site: IN2P3-IRES, VO: vo.access.egi.eu, command: volume list --name my-volume
+--------------------------------------+-----------+-----------+------+-------------+
| ID                                   | Name      | Status    | Size | Attached to |
+--------------------------------------+-----------+-----------+------+-------------+
| aa711296-5cff-46ac-bbe3-58e00712ee3e | my-volume | available |   10 |             |
+--------------------------------------+-----------+-----------+------+-------------+

When the status of the volume is available the volume is ready to be attached to a VM.

See volume details

To view details of a volume use the FedCloud command below:

Tip

The volume can be specified either by its ID or by its name (if it has one).

$ fedcloud openstack volume show Matlab
Site: IN2P3-IRES, VO: vo.access.egi.eu, command: volume show Matlab
+------------------------------+------------------------------------------------------------+
| Field                        | Value                                                      |
+------------------------------+------------------------------------------------------------+
| attachments                  | [{'server_id': 'a4ab00a1-d458-41a9-a091-ee707bc9357e',     |
|                              |   'attachment_id': '291111d3-f43c-494c-b64c-5c0abcda3d37', |
|                              |   'attached_at': '2021-08-05T08:50:19.000000',             |
|                              |   'host_name': 'sbgcsrv17.in2p3.fr',                       |
|                              |   'volume_id': '9a4000fb-0bcc-47e8-96fb-85a222295402',     |
|                              |   'device': '/dev/vdb',                                    |
|                              |   'id': '9a4000fb-0bcc-47e8-96fb-85a222295402'}]           |
| availability_zone            | nova                                                       |
| bootable                     | false                                                      |
| consistencygroup_id          | None                                                       |
| created_at                   | 2021-08-05T08:48:41.000000                                 |
| description                  |                                                            |
| encrypted                    | False                                                      |
| id                           | 9a4000fb-0bcc-47e8-96fb-85a222295402                       |
| multiattach                  | False                                                      |
| name                         | Matlab                                                     |
| os-vol-tenant-attr:tenant_id | 7a910xxxxae74ed9yyyy7497zzzz9499                           |
| properties                   |                                                            |
| replication_status           | None                                                       |
| size                         | 50                                                         |
| snapshot_id                  | None                                                       |
| source_volid                 | None                                                       |
| status                       | in-use                                                     |
| type                         | ceph                                                       |
| updated_at                   | 2021-08-05T08:50:20.000000                                 |
| user_id                      | babzz8c3b4cxxxx6286dacyyyy01e5a3                           |
+------------------------------+------------------------------------------------------------+

Attach volume to VM

Mapping block devices to VMs is described in detail in the OpenStack documentation.

To attach a volume to a VM use the FedCloud command below:

Note

To be able to attach a volume to a VM, the volume must not be attached to any VM (volume status must be available).

Caution

The optional --device argument to specify the device name in the VM should not be used. It does not work properly, and will be removed in the near future.

$ fedcloud openstack server add volume my-server my-volume
Site: IN2P3-IRES, VO: vo.access.egi.eu, command: server add volume my-server my-volume

You can check that the volume got attached to the VM (and with what device name) by either looking at the details of the volume, the details of the VM, or by listing only the volume in question (filter by volume name or ID):

$ fedcloud openstack volume list --name my-volume
Site: IN2P3-IRES, VO: vo.access.egi.eu, command: volume list --name my-volume
+--------------------------------------+-----------+-----------+------+-----------------------+
| ID                                   | Name      | Status    | Size | Attached to           |
+--------------------------------------+-----------+-----------+------+-----------------------+
| aa711296-5cff-46ac-bbe3-58e00712ee3e | my-volume | in-use    |   10 | my-server on /dev/vdc |
+--------------------------------------+-----------+-----------+------+-----------------------+

When the volume status is in-use the volume is attached to a VM, and it can be used from the VM.

Detach volume from VM

To detach a volume from a VM use the FedCloud command below:

$ fedcloud openstack server remove volume my-server my-volume
Site: IN2P3-IRES, VO: vo.access.egi.eu, command: server remove volume my-server my-volume

You can check that the volume got detached by either looking at the details of the volume, the details of the VM, or by listing only the volume in question (filter by volume name or ID):

$ fedcloud openstack volume list --name my-volume
Site: IN2P3-IRES, VO: vo.access.egi.eu, command: volume list --name my-volume
+--------------------------------------+-----------+-----------+------+-------------+
| ID                                   | Name      | Status    | Size | Attached to |
+--------------------------------------+-----------+-----------+------+-------------+
| aa711296-5cff-46ac-bbe3-58e00712ee3e | my-volume | available |   10 |             |
+--------------------------------------+-----------+-----------+------+-------------+

When the volume status is available the volume is not attached to any VM.

Resize volume

To resize a volume set its size property to the desired size. For example, if there is a volume named my-volume with a size of 10GB, it can be resized using the FedCloud command below:

Tip

Other volume properties can be altered in the same way.

Note

To be able to resize a volume, the volume must not be attached to any VM (volume status must be available), unless the volume driver supports in-use extend.

$ fedcloud openstack volume set --size 20 my-volume
Site: IN2P3-IRES, VO: vo.access.egi.eu, command: volume set --size 20 my-volume

You can check that the volume got resized by either looking at the details of the volume, or by listing only the volume in question (filter by volume name or ID):

$ fedcloud openstack volume list --name my-volume
Site: IN2P3-IRES, VO: vo.access.egi.eu, command: volume list --name my-volume
+--------------------------------------+-----------+-----------+------+-------------+
| ID                                   | Name      | Status    | Size | Attached to |
+--------------------------------------+-----------+-----------+------+-------------+
| aa711296-5cff-46ac-bbe3-58e00712ee3e | my-volume | available |   20 |             |
+--------------------------------------+-----------+-----------+------+-------------+

Snapshot a volume

Users can create snapshots of a volume that can later be used to create other volumes or to rollback to a precedent point in time. Volume snapshots are pointers in the read-write history of a volume.

To take a snapshot of a volume, use the FedCloud command below:

Tip

See also the documentation about the other snapshot management commands.

Note

To be able to create a snapshot of a volume, the volume must not be attached to any VM (volume status must be available). To create a snapshot while the volume is attached to a VM, use the --force command flag, but be aware that there may be inconsistencies if the VM’s OS is not aware of the snapshot being taken.

$ fedcloud openstack volume snapshot create --volume my-volume my-snapshot --force
Site: IN2P3-IRES, VO: vo.access.egi.eu, command: volume snapshot create --volume my-volume my-snapshot
+-------------+--------------------------------------+
| Field       | Value                                |
+-------------+--------------------------------------+
| created_at  | 2021-08-06T16:08:37.631226           |
| description | None                                 |
| id          | 15149b42-032f-4cec-b6f3-41aa5c958081 |
| name        | my-snapshot                          |
| properties  |                                      |
| size        | 10                                   |
| status      | creating                             |
| updated_at  | None                                 |
| volume_id   | aa711296-5cff-46ac-bbe3-58e0712ee3e9 |
+-------------+--------------------------------------+

The status of the snapshot will probably be returned as creating. To check if the snapshot is ready, look at the details of the snapshot, or list only the newly created snapshot (filter by snapshot name or ID):

$ fedcloud openstack volume snapshot list --name my-snapshot
Site: IN2P3-IRES, VO: vo.access.egi.eu, command: volume snapshot list --name my-snapshot
+--------------------------------------+-------------+-------------+-----------+------+
| ID                                   | Name        | Description | Status    | Size |
+--------------------------------------+-------------+-------------+-----------+------+
| 15149b42-032f-4cec-b6f3-41aa5c958081 | my-snapshot | None        | available |   10 |
+--------------------------------------+-------------+-------------+-----------+------+

When the status of the snapshot is available the snapshot is ready, and can be used to create new volumes or to restore the source volume to the point-in-time when the snapshot was taken.

Backup a volume

Users can also create backups of a volume, but backups can only be used later to create or replace other volumes. A volume backup is a copy of a volume saved to cold storage, which is cheaper than the performant storage used for volumes and snapshots.

To make a backup of a volume, use the FedCloud command below:

Tip

See also the documentation of the other backup management commands.

Note

Not all OpenStack deployments support volume backups.

Note

Backups use as much storage as the source volume, albeit in a cheaper storage layer. This means backups take a long time to create (~4h for 500GB), and the space is accounted for the same way as for regular volumes (the entire size of the backed up volume, regardless of how much of the volume space is actually used). Thus backups should be deleted when no longer needed.

Note

To be able to make a backup of a volume, the volume must not be attached to any VM (volume status must be available). To make a backup while the volume is attached to a VM, use the --force command flag, but be aware that there may be inconsistencies if the VM’s OS is not aware of the backup being taken.

$ fedcloud openstack volume backup create --name my-backup my-volume --force
Site: IN2P3-IRES, VO: vo.access.egi.eu, command: volume backup create --name my-backup my-volume
+-------------+--------------------------------------+
| Field       | Value                                |
+-------------+--------------------------------------+
| created_at  | 2021-08-06T16:08:37.631226           |
| description | None                                 |
| id          | 158bcb42-032f-4cec-b6f3-890a5c958081 |
| name        | my-backup                            |
| properties  |                                      |
| size        | 10                                   |
| status      | creating                             |
| updated_at  | None                                 |
| volume_id   | aa711296-5cff-46ac-bbe3-58e0712ee3e9 |
+-------------+--------------------------------------+

The status of the backup will probably be returned as creating. To check if the backup has finished, look at the details of the backup, or list only the newly created backup (filter by backup name or ID):

$ fedcloud openstack volume backup list --name my-backup
Site: IN2P3-IRES, VO: vo.access.egi.eu, command: volume backup list --name my-backup
+--------------------------------------+-----------+-------------+-----------+------+
| ID                                   | Name      | Description | Status    | Size |
+--------------------------------------+-----------+-------------+-----------+------+
| 158bcb42-032f-4cec-b6f3-890a5c958081 | my-backup | None        | available |   10 |
+--------------------------------------+-----------+-------------+-----------+------+

When the status of the backup is available the backup operation is complete.

Delete volume

To delete a volume use the following FedCloud command:

Note

To be able to delete a volume, the volume must not be attached to any VM (volume status must be available).

$ fedcloud openstack volume delete my-volume
Site: IN2P3-IRES, VO: vo.access.egi.eu, command: volume delete my-volume

This starts deletion of the specified volume (the volume status changes to deleting):

$ fedcloud openstack volume list --name my-volume
Site: IN2P3-IRES, VO: vo.access.egi.eu, command: volume list --name my-volume
+--------------------------------------+-----------+----------+------+-------------+
| ID                                   | Name      | Status   | Size | Attached to |
+--------------------------------------+-----------+----------+------+-------------+
| aa711296-5cff-46ac-bbe3-58e00712ee3e | my-volume | deleting |   10 |             |
+--------------------------------------+-----------+----------+------+-------------+

Once deletion of the specified volume is complete, it will no longer show up in the list of volumes.

Access from your VMs

Block storage volumes attached to a VM will appear as a block device in the VM.

To find out the device name that got assigned to a volume when it was attached to a VM, look at the details of the volume, or list only the volume in question (filter by volume name or ID):

$ fedcloud openstack volume list --name my-volume
Site: IN2P3-IRES, VO: vo.access.egi.eu, command: volume list --name my-volume
+--------------------------------------+-----------+--------+------+-----------------------+
| ID                                   | Name      | Status | Size | Attached to           |
+--------------------------------------+-----------+--------+------+-----------------------+
| aa711296-5cff-46ac-bbe3-58e00712ee3e | my-volume | in-use |   10 | my-server on /dev/vdb |
+--------------------------------------+-----------+--------+------+-----------------------+

In this example the device name is /dev/vdb. To validate this, run the following command in the VM:

$ lsblk
NAME   MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
vda    252:0    0  20G  0 disk
└─vda1 252:1    0  20G  0 part /
vdb    252:16   0  10G  0 disk

Usually these devices are empty upon creation. The first time you attach them to a VM, you will need to partition the device and create filesystem(s) on it, by running the following command in the VM:

Tip

Using a file system volume label is useful to avoid the need to find the out the device name, especially when multiple block storage volumes are attached to a VM. It is recommended to use a file system volume label in the VM that is the same as the name of the block storage volume.

Tip

The filesystem type can be one supported by the Linux distribution in the VM, but xfs and ext4 are the most widely used.

Caution

Only run this command the first time you use the device, as it deletes all data! Make sure you use the correct device name, otherwise you will destroy data on other devices!

$ sudo mkfs.ext4 -L my-volume /dev/vdb

Once you created a filesystem on the device, you can mount it at any desired path by running the following command in the VM:

$ sudo mount /dev/vdb1 /<path>

Continuing with the example above, if we check again the block devices by running the following command in the VM:

$ lsblk
NAME   MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
vda    252:0    0  20G  0 disk
└─vda1 252:1    0  20G  0 part /
vdb    252:16   0  10G  0 disk
└─vdb1 252:1    0  10G  0 part /<path>

If non-root users should be able to access the mounted volume similar to the way e.g. /tmp is accessible, set the sticky bit on the mount point, with this command in the VM:

$ sudo chmod +t /<path>

If the desired behaviour is to mount the file system automatically on VM restart, add it to /etc/fstab. Using the LABEL parameter will ensure the correct volume is chosen if multiple volumes are attached:

LABEL=my-volume /<path> ext4 noatime,nodiratime,user_xattr,nofail 0 0

Note

The use of option nofail is recommended in order to skip (and not block on) mounting the file system volume if it is unavailable, e.g. in case of network issues. Remove this option from the fstab line if you want the VM to block the boot process if the volume is unavailable.

Note

The use of option nobarrier is not recommended as volumes are accessed via a cache, and ignoring the correct ordering of journal commits may result in a corrupted file system in case of a hardware problem.

With that you can access /<path> inside the VM, where all data stored on the volume will be available. Applications will not see any difference between a block storage device and a regular disk, thus no major changes should be required in the application logic.

Storage Encryption

This section describes the usage of the tool cryptsetup to enable the permanent encryption of the data stored in the disk. The tool is available in standard linux distributions, and for this guide we assume the installation in an Ubuntu distribution.

$ sudo su -
$ apt -y install cryptsetup

To encrypt the disk, it must be first initialized correctly. In the example below, the disk named /dev/vdb is first filled with random data and then initialized using the cryptsetup luksFormat command below. This first step can be quite long.

$ dd if=/dev/urandom of=/dev/vdb bs=4k
$ cryptsetup -v --cipher aes-xts-plain64 --key-size 512 --hash sha512 \
    --iter-time 5000 --use-random luksFormat /dev/vdb

If this last command slows down or even blocks with the following message:

System is out of entropy while generating volume key.
Please move mouse or type some text in another window to gather some random events.
Generating key (0% done).

you can make the cryptsetup luksFormat command running faster by first installing the haveged program in your virtual machine.

The following command verifies that the disk is now of type LUKS:

$ cryptsetup luksDump /dev/vdb
LUKS header information for /dev/vdb

Version:        1
Cipher name:    aes
Cipher mode:    xts-plain64
Hash spec:      sha512
Payload offset: 4096
MK bits:        512
MK digest:      c4 f7 4b 02 2a 3f 12 c1 2c ba e5 c9 d2 45 9a cd 89 20 6c 73
MK salt:        98 58 3e f3 f6 88 99 ea 2a f3 cf 71 a0 0d e5 8b
                d5 76 64 cb d2 5c 9b d1 8a d3 1d 18 0e 04 7a eb
MK iterations:  81250
UUID:           c216d954-199e-4eab-a167-a3587bd41cb3

Key Slot 0: ENABLED
    Iterations:             323227
    Salt:                   a0 45 3e 98 fa cf 60 74 c6 09 3d 54 97 89 be 65
                            5b 96 7c 1c 39 26 47 b4 8b 0e c1 3a c9 94 83 c2
    Key material offset:    8
    AF stripes:             4000
Key Slot 1: DISABLED
Key Slot 2: DISABLED
Key Slot 3: DISABLED
Key Slot 4: DISABLED
Key Slot 5: DISABLED
Key Slot 6: DISABLED
Key Slot 7: DISABLED

The disk is now ready for use. The first time you use it, you must perform the following steps:

Step 1: Open the encrypted disk with the cryptsetup luksOpen command. The name storage1 is only indicative, you can choose what you want:

$ cryptsetup luksOpen /dev/vdb storage1

Step 2: Create a filesystem on disk:

$ mkfs.ext4 /dev/mapper/storage1

Step 3: Create the disk mount point:

$ mkdir /storage1

Step 4: Mount the disk:

$ mount -t ext4 /dev/mapper/storage1 /storage1

Step 5: Check available space (this may be slightly different from what was entered during the openstack volume create command):

$ df -h /storage1
Filesystem            Size  Used Avail Use% Mounted on
/dev/mapper/storage1  2.0G  6.0M  1.9G   1% /storage1

Once the disk is operational, steps 2 and 3 are no longer necessary.

You can now send files (for example DATA.dat) from your personal computer to your virtual machine in a secure way, for example with scp:

$ scp -i ${HOME}/.ssh/cloudkey DATA.dat ubuntu@134.158.151.224:/storage1
DATA.dat                               100%   82     0.1KB/s   00:00

When you are done with your work on the disk, you can remove it cleanly with the following commands:

$ umount /storage1
$ cryptsetup close storage1

For subsequent uses of the persistent disk, there will be no need to perform all these operations, only the following are necessary:

$ cryptsetup luksOpen /dev/vdb storage1
$ mkdir -p /storage1
$ mount -t ext4 /dev/mapper/storage1 /storage1

Note that directory /storage1 will be created only if it does not already exist.

Access via EGI Data Transfer

EGI Data Transfer allows you to move any type of data files asynchronously from one storage to another. If you want to copy data from/to one VM running on the EGI cloud, you will need to run a compatible server (Webdav/HTTPS, GridFTP, xrootd, SRM, S3, GCloud) that can interact with the FTS3 software.

An easy way to provide a GridFTP server on your VM is to use the gridftp-le ready2go docker stack for deploying a GridFTP Docker Container with certificates from Let’s Encrypt. Take into account:

Security groups for the VM must allow ports 80, 2811 and the 50000-50200 range.
The VM must have a valid DNS entry (you can use Dynamic DNS in FedCloud to get one)
The default setup uses /srv as path to expose and maps users to the nobody user. Make sure that nobody is able to read (and write if needed) on that location or set the mapping to the appropriate users.
The Let’s Encrypt certificates may not be accepted by some of the EGI infrastructure endpoints, you may want to consider using IGTF certificates instead. Check your CA for instructions on how to get those.
You can add direct mappings for specific DNs by adding a /etc/localgridmap.conf file in your running container. See the example below to map the /DC=org/DC=terena/DC=tcs/C=NL/O=Stichting EGI/CN=Enol Fernandez del Castillo DN to nobody. You can add as many lines as needed:
```
"/DC=org/DC=terena/DC=tcs/C=NL/O=Stichting EGI/CN=Enol Fernandez del Castillo" nobody
```
You need to specify the environment variables in the docker-compose.yml file for obtaining the Let’s Encrypt certificate. An extra variable GLOBUS_HOSTNAME must be also set:
```
environment:
  - TESTCERT
  - EMAIL=youremail@domain.com
  - DOMAIN=mygridftp.example.com
  - GLOBUS_HOSTNAME=mygridftp.example.com
```
If you are running on a site with MTU smaller than 1500 (e.g. CESNET-MCC), make sure that you set the MTU to a value smaller than the interface MTU(you can check this with ip addr). In your docker-compose.yml, add:
```
networks:
  default:
    driver: bridge
    driver_opts:
      com.docker.network.driver.mtu: 1434
```

Last modified March 8, 2023 by Baptiste Grenier : Import a GitHub action to check spell (#584)