system-config/doc/source/sysadmin.rst

title

System Administration

This page collects technical information of relevance to those interested in admin of OpenDev services. For a higher-level overview, see opendev-infra-overview.

System Administration

SSH Access

For any of the systems managed by the OpenDev Infrastructure team, the following practices must be observed for SSH access:

• SSH access is only permitted with SSH public/private key authentication.
• Users must use a strong passphrase to protect their private key. A passphrase of several words, at least one of which is not in a dictionary is advised, or a random string of at least 16 characters.
• To mitigate the inconvenience of using a long passphrase, users may want to use an SSH agent so that the passphrase is only requested once per desktop session.
• Users private keys must never be stored anywhere except their own workstation(s). In particular, they must never be stored on any remote server.
• If users need to 'hop' from a server or bastion host to another machine, they must not copy a private key to the intermediate machine (see above). Instead SSH agent forwarding may be used. However due to the potential for a compromised intermediate machine to ask the agent to sign requests without the users knowledge, in this case only an SSH agent that interactively prompts the user each time a signing request (ie, ssh-agent, but not gnome-keyring) is received should be used, and the SSH keys should be added with the confirmation constraint ('ssh-add -c').
• The number of SSH keys that are configured to permit access to OpenDev machines should be kept to a minimum.
• OpenDev Infrastructure machines must use Ansible to centrally manage and configure user accounts, and the SSH authorized_keys files from the opendev/system-config repository.
• SSH keys should be periodically rotated (at least once per year). During rotation, a new key can be added to puppet for a time, and then the old one removed.

Gerrit Admins

To provide a reasonable firewall from outside authentication systems, Gerrit administrators keep two accounts: one for normal code review activity and one for performing Gerrit administration. Following the same pattern as our Kerberos administrator account logins, the admin account corresponding to $USER would be $USER.admin (Gerrit doesn't allow / in usernames) so they can be easily identified when auditing activity. Unlike the normal code review account, the admin account should have no OpenID so that it is only accessable by API/CLI methods so they cannot be compromised at the third-party ID provider.

To create a personal Gerrit admin account from a shell on the server, run the following command

$ sudo -u gerrit2 ssh -i ~gerrit2/review_site/etc/ssh_host_rsa_key -p 29418 -l 'Gerrit Code Review' localhost "suexec --as openstack-project-creator -- gerrit create-account --group Administrators --full-name myname.admin --ssh-key 'ssh-rsa AAAA...BCDE myname@computer' myname.admin"

We suexec as the openstack-project-creator account because the magic Gerrit Code Review pseudoaccount can't set group memberships so we need to run that command as a user which is already in the Administrators group. With an account like this, routine actions like populating new groups with initial members is still quite simple

$ ssh -p 29418 myname.admin@review.opendev.org "gerrit set-members some-new-group --add somebody@example.org"

Another common example is bypassing Zuul to submit a change for merging directly to a project. See force-merging-a-change for details.

GitHub Access

To ensure that code review and testing are not bypassed in the public Git repositories, only Gerrit will be permitted to commit code to OpenDev repositories. Because GitHub always allows project administrators to commit code, accounts that have access to manage the GitHub projects necessarily will have commit access to the repositories.

A shared Github administrative account is available (credentials stored in the global authentication location). If administrators would prefer to keep a separate account, it can be added to the organisation after discussion and noting the caveats around elevated access. The account must have 2FA enabled.

In either case, the administrator accounts should not be used to check out or commit code for any project.

Note that it is unlikely to be useful to use an account also used for active development, as you will be subscribed to many notifications for all projects.

Root only information

Below is information relevant to members of the core team with root access.

Accessing Clouds

As an unprivileged user who is a member of the sudo group on bridge, you can inspect any of the clouds with

$ sudo openstack --os-cloud <cloud name> --os-cloud-region <region name>

Backups

Infra uses the borg backup tool.

Hosts in the borg-backup Ansible inventory group will be backed up to servers in the borg-backup-server group with borg. The playbooks/roles/borg-backup and playbooks/roles/borg-backup-server roles implement the required setup.

The backup server has a unique Unix user for each host to be backed up. The roles will setup required users, their home directories in the backup volume and relevant authorized_keys.

Host backup happens via a daily cron job (managed by Ansible) on each individual host to be backed up. The host to be backed up initiates the backup process to the remote backup server(s) using a separate ssh key setup just for backup communication (see /root/.ssh/config).

Setting up hosts for backup

To setup a host for backup, put it in the borg-backup group.

Hosts can specify borg_backup_excludes_extra and borg_backup_dirs_extra to exclude or include specific directories as required (see role documentation for more details).

borg splits backup data into chunks and de-duplicates as much as possible. For backing up large items, particularly things like database dumps, we want to give borg as much chance to de-duplicate as possible. Approaches such as dumping to compressed files on disk defeat de-duplication because all the data changes for each dump.

For dumping large data, hosts should put a file into /etc/borg-streams that performs the dump in an uncompressed manner to stdout. The backup scripts will create a separate archive for each stream defined here. For more details, see the backup role documentation. These streams should attempt to be as friendly to de-duplication as possible; see some of the examples of mysqldump to find arguments that help keep the output data more stable (and hence more easily de-duplicated).

Restore from Backup

Hosts have /usr/local/bin/borg-mount (specify one of the backup servers as an argument) that will mount the backups to /opt/backups via FUSE.

borg has other options for restoring. If you need to extract on the backup server itself, a basic way to dump a host at a particular time is to

• log into the backup server
• sudo su - to switch to the backup user for the host to be restored
• you will now be in the home directory of that user
• run /opt/borg/bin/borg list ./backup to list the archives available
• these should look like <hostname>-<stream>-YYYY-MM-DDTHH:MM:SS
• move to working directory
• extract one of the appropriate archives with /opt/borg/bin/borg extract ~/backup <archive-tag>

Managing backup storage

We run borg in append-only mode. This means clients can not remove old backups on the server.

However, due to the way borg works, append-only mode plays all client transactions into a transaction log until a read-write operation occurs. Examining the repository will appear to have all these transactions applied (e.g. pruned archives will not appear; even if they have not actually been pruned from disk). If you have reason to not trust the state of the backup, you should not run any read-write operations. You will need to manually examine the transaction log and roll-back to a known good state; see https://borgbackup.readthedocs.io/en/stable/usage/notes.html#append-only-mode.

However, we have limited backup space. Each backup server has a script /usr/local/bin/prune-borg-backups which can be run to reclaim space. This should be run in a screen instance as it can take a considerable time. It will prompt when run; you can confirm the process with a noop run; confirming the prune will log the output to /opt/backups. This will keep the last 7 days of backups, then monthly backups for 1 year and yearly backups for each archive. The backup servers will send a warning when backup volume usage is high, at which point this can be run manually.

Force-Merging a Change

Occasionally it is necessary to bypass the CI system and merge a change directly. Usually, this is only required if we have a hole in our testing of the CI or related systems themselves and have merged a change which causes them to be unable to operate normally and therefore unable to merge a reversion of the problematic change. In these cases, use the following procedure to force-merge a change.

• Add yourself to the Project Bootstrappers group in Gerrit.

$ ssh -p 29418 myname.admin@review.opendev.org \
  "gerrit set-members 'Project Bootstrappers' --add myname.admin"

• Navigate to the change which needs to be merged and reload the page.

• Remove any -2 votes on the change.

• Add +2 Code-Review, and +1 Workflow votes if necessary, then add +2 Verified. Also leave a review comment briefly explaining why this was necessary, and make sure to mention it in the #opendev IRC channel (ideally as a #status log entry for the benefit of those not paying close attention to scrollback).

• At this point, a Submit Button should appear, click it. The change should now be merged.

  $ ssh -p 29418 myname.admin@review.opendev.org "gerrit review 12345,6 --message 'Bypassing Zuul to merge this.' --code-review=2 --verified=2 --label workflow=1 --submit"

• Remove yourself from Project Bootstrappers

  $ ssh -p 29418 myname.admin@review.opendev.org "gerrit set-members 'Project Bootstrappers' --remove myname.admin"

This procedure is the safest way to force-merge a change, ensuring that all of the normal steps that Gerrit performs on repos still happen.

Note that it's possible to temporarily add your normal OpenID-associated WebUI account to the Administrators group or other groups with similar superuser permissions like Project Bootstrappers, but keep in mind that an attacker who has quietly gained control of your account at the OpenID provider could be waiting for that opportunity to take advantage of the added permissions, or you may simply forget to remove the account afterward negating the added safety of this account separation.

For more examples, see the detailed documentation for Gerrit's SSH CLI, available on our server: https://review.opendev.org/Documentation/cmd-index.html

Launching New Servers

New servers are launched using the launch/launch-node.py tool from the git repository https://opendev.org/opendev/system-config. This tool is run from a checkout on the bridge - please see :git_file:`launch/README.rst` for detailed instructions.

Disable/Enable Ansible

You should normally not make manual changes to servers, but instead, make changes through ansible or puppet. However, under some circumstances, you may need to temporarily make a manual change to a managed resource on a server.

OpenDev uses a Static Inventory in Ansible to control execution of Ansible on hosts. A full understanding of the concepts in Ansible Inventory Introduction is essential for being able to make informed decisions about actions to take.

In the case of needing to disable the running of ansible or puppet on a node, it's a simple matter of adding an entry to the ansible inventory "disabled" group in :git_file:`inventory/groups.yaml. The disabled entry is an input to `ansible --list-hosts so you can check your entry simply by running it with ansible $hostlist --list-hosts as root on the bridge host and ensuring that the list of hosts returned is as expected. Globs, group names and server UUIDs should all be acceptable input.

If you need to disable a host immediately without waiting for a patch to land to system-config, there is a file on the bridge host, /etc/ansible/hosts/emergency.yaml that can be edited directly.

/etc/ansible/hosts/emergency.yaml is a file that should normally be empty, but the contents are not managed by ansible. It's purpose is to allow for disabling ansible at times when landing a change to the ansible repo would be either unreasonable or impossible.

Disabling puppet via ansible inventory does not disable puppet from being able to be run directly on the host, it merely prevents ansible from attempting to run it during the regular zuul jobs. If you choose to run puppet manually on a host, take care to ensure that it has not been disabled at the bridge level first.

If you need to pause all execution of ansible playbooks by Zuul you can run the utility script disable-ansible. The script touches the file /home/zuul/DISABLE-ANSIBLE on bridge.openstack.org. Doing this forces the Zuul jobs that run ansible for us to wait until that file is removed. This acts like a global pause. The script exists to prevent admins from misspelling the name of the file and is recommended.

Examples

To disable an OpenDev instance called foo.opendev.org temporarily, ensure the following is in /etc/ansible/hosts/emergency.yaml

# Please add an inline comment so we know who added the host and why
plugin: yamlgroup
groups:
  disabled:
    - foo.opendev.org # 2020-05-23 bob is testing change 654321

Ad-hoc Ansible runs

If you need to run Ansible manually against a host, you should

• disable automated Ansible runs following the section above
• su to the zuul user and run the playbook with something like ansible-playbook -vv src/opendev.org/opendev/system-config/playbooks/service-<name>.yaml
• Restore automated ansible runs.
• You can also use the --limit flag to restrict which hosts run when there are many in a group. However, be aware that some roles/playbooks like letsencrypt and backup run across multiple hosts (deploying DNS records or authorization keys), so incorrect --limit flags could cause further failures.

Cinder Volume Management

Adding a New Device

If the main volume group doesn't have enough space for what you want to do, this is how you can add a new volume.

Log into bridge.openstack.org and run:

export OS_CLOUD=openstackci-rax
export OS_REGION_NAME=DFW

openstack server list
openstack volume list

Change the variables to use a different environment. ORD for example:

export OS_CLOUD=openstackci-rax
export OS_REGION_NAME=ORD

• Add a new 1024G cinder volume (substitute the hostname and the next number in series for NN):

  openstack volume create --size 1024 "$HOSTNAME.ord.openstack.org/mainNN"
  openstack server add volume "HOSTNAME.openstack.org" "HOSTNAME.openstack.org/mainNN"

• or to add a 100G SSD volume:

  openstack volume create --type SSD --size 100 "HOSTNAME.openstack.org/mainNN"
  openstack server add volume "HOSTNAME.openstack.org" "HOSTNAME.openstack.org/mainNN"

• Then, on the host, create the partition table:

  DEVICE=/dev/xvdX
  sudo parted $DEVICE mklabel msdos mkpart primary 0% 100% set 1 lvm on
  sudo pvcreate ${DEVICE}1

• It should show up in pvs:

  $ sudo pvs
    PV         VG   Fmt  Attr PSize    PFree
    /dev/xvdX1      lvm2 a-   1024.00g 1024.00g

• Add it to the main volume group:

  sudo vgextend main ${DEVICE}1

• However, if the volume group does not exist yet, you can create it:

  sudo vgcreate main ${DEVICE}1

Creating a New Logical Volume

Make sure there is enough space in the volume group:

$ sudo vgs
  VG   #PV #LV #SN Attr   VSize VFree
  main   4   2   0 wz--n- 2.00t 347.98g

If not, see Adding a New Device.

Create the new logical volume and initialize the filesystem:

NAME=newvolumename
sudo lvcreate -L1500GB -n $NAME main

sudo mkfs.ext4 -m 0 -j -L $NAME /dev/main/$NAME
sudo tune2fs -i 0 -c 0 /dev/main/$NAME

Be sure to add it to /etc/fstab.

Expanding an Existing Logical Volume

Make sure there is enough space in the volume group:

$ sudo vgs
  VG   #PV #LV #SN Attr   VSize VFree
  main   4   2   0 wz--n- 2.00t 347.98g

If not, see Adding a New Device.

The following example increases the size of a volume by 100G:

NAME=volumename
sudo lvextend -L+100G /dev/main/$NAME
sudo resize2fs /dev/main/$NAME

The following example increases the size of a volume to the maximum allowable:

NAME=volumename
sudo lvextend -l +100%FREE /dev/main/$NAME
sudo resize2fs /dev/main/$NAME

Replace an Existing Device

We generally need to do this if our cloud provider is planning maintenance to a volume. We usually get a few days heads up on maintenance window, so depending on the size of the volume, it may take some time to replace.

First thing to do is add the replacement device to the server, see Adding a New Device. Be sure the replacement volume is the same type / size as the existing.

If the step above were followed, you should see something like:

$ sudo pvs
  PV         VG   Fmt  Attr PSize  PFree 
  /dev/xvdb1 main lvm2 a--  50.00g     0 
  /dev/xvdc1 main lvm2 a--  50.00g 50.00g

Be sure both devices are in the same VG (volume group), if not you did not properly extend the device.

Note

Be sure to use a screen session for the following step!

Next is to move the data from once device to another:

$ sudo pvmove /dev/xvdb1 /dev/xvdc1
  /dev/xvdb1: Moved: 0.0%
  /dev/xvdb1: Moved: 1.8%
  ...
  ...
  /dev/xvdb1: Moved: 99.4%
  /dev/xvdb1: Moved: 100.0%

Confirm all the data was moved, and the original device is empty (PFree):

$ sudo pvs
  PV         VG   Fmt  Attr PSize  PFree 
  /dev/xvdb1 main lvm2 a--  50.00g 50.00g
  /dev/xvdc1 main lvm2 a--  50.00g     0 

And remove the device from the main volume group:

$ sudo vgreduce main /dev/xvdb1
  Removed "/dev/xvdb1" from volume group "main"

To be safe, we can also wipe the label from LVM:

$ sudo pvremove /dev/xvdb1
  Labels on physical volume "/dev/xvdb1" successfully wiped

Leaving us with just a single device:

$ sudo pvs
  PV         VG   Fmt  Attr PSize  PFree
  /dev/xvdc1 main lvm2 a--  50.00g    0 

At this time, you are able to remove the original volume from openstack if no longer needed.

Email

There is a shared email account used for Infrastructure related mail (account sign-ups, support tickets, etc). Root admins should ensure they have access to this account; access credentials are available from any existing member.