library-syncer

This project aims to ease some of the pains encountered when attempting to sync VM templates in a VMware vSphere Content Library to a large number of geographically-remote sites under less-than-ideal networking conditions.

Overview

The solution leverages lightweight Docker containers in server and client roles. The servers would be deployed at the primary datacenter(s), and the clients at the remote sites. The servers make a specified library folder available for the clients to periodically synchronize using rsync over SSH, which allows for delta syncs so that bandwidth isn't wasted transferring large VMDK files when only small portions have changed.

Once the sync has completed, each client runs a Python script to generate/update a Content Library JSON manifest which is then published over HTTP/HTTPS (courtesy of Caddy). Traditional Content Libraries at the local site can connect to this as a subscribed library to make the synced items available within vSphere.

After the initial, immediate sync, subsequent syncs are initiated through a cron scheduled task.

The rough architecture looks something like this:

                        |
     PRIMARY SITE       |      REMOTE SITES      +----------------------------+
                        |                        |          vSphere           |
                        |    +----------------+  |   +--------------------+   |
                        |    |                |  |   |                    |   |
                        |    | library-syncer |  |   | subscribed content |   |
                     +--+--->|                +--+-->|                    |   |
                     |  |    |    client      |  |   |      library       |   |
                     |  |    |                |  |   |                    |   |
                     |  |    +----------------+  |   +--------------------+   |
                     |  |                        |                            |
+-----------------+  |  |    +----------------+  |   +--------------------+   |
|                 |  |  |    |                |  |   |                    |   |
|  library-syncer |  |  |    | library-syncer |  |   | subscribed content |   |
|                 +--+--+--->|                +--+-->|                    |   |
|     server      |  |  |    |    client      |  |   |      library       |   |
|                 |  |  |    |                |  |   |                    |   |
+-----------------+  |  |    +----------------+  |   +--------------------+   |
                     |  |                        |                            |
                     |  |    +----------------+  |   +--------------------+   |
                     |  |    |                |  |   |                    |   |
                     |  |    | library-syncer |  |   | subscribed content |   |
                     +--+--->|                +--+-->|                    |   |
                        |    |    client      |  |   |      library       |   |
                        |    |                |  |   |                    |   |
                        |    +----------------+  |   +--------------------+   |
                        |                        +----------------------------+

Prerequisites

Docker and docker-compose

You'll need Docker (and preferably also docker-compose) on both the server and client VMs. Installing and configuring Docker is beyond the scope of this document as it will largely depend on what operating system you settle on for the Docker hosts.

SSH keypair for rsync user

The server image includes a syncer user account which the clients will use to authenticate over SSH. This account is locked down and restricted with rrsync to only be able to run rsync commands. All that you need to do is generate a keypair for the account to use:

ssh-keygen  -t rsa -b 4096 -N "" -f id_syncer

TLS certificate pair (optional)

By default, the client will publish its library over HTTP. If you set the TLS_NAME environment variable to the server's publicly-accessible FQDN, the Caddy web server will automatically retrieve and apply a certificate issued by Let's Encrypt. For deployments on internal networks which need to use a certificate issued by an internal CA, you can set TLS_CUSTOM_CERT=true and add the private key and certificate to the clients - more on that in a minute.

You can generate the cert signing request and key in one shot like this:

openssl req -new \
-newkey rsa:4096 -nodes -keyout library.example.com.key \
-out library.example.com.csr \
-subj "/C=US/ST=Somestate/L=Somecity/O=Example.com/OU=LAB/CN=library.example.com"

Usage

Server

Preparation

VM templates should be stored on the Docker host in its own folder under the ./data/library/ path. These should be in OVF format, not OVA format, so that they can be made available in the vSphere inventory on the remote side.

(For extra credit, you can export the ./data/library/ path as an NFS share, mount that as a datastore in vSphere, and create a new local Content Library atop that. This would make it an easy target for a CI/CD pipeline to crank out new/updated templates on a regular schedule, and those would then be automatically available to the library-syncer clients without any additional effort. Just a thought.)

The server also needs the id_syncer.pub public key which was generated earlier. Place it in the ./data/ssh/ folder.

Example folder structure:

.
├── data
│   ├── library
|   |   ├── Template_1
|   |   |   ├── template_1.ovf
|   |   |   └── template_1.vmdk 
|   |   ├── Template_2
|   |   |   ├── template_2.ovf
|   |   |   └── template_2.vmdk 
│   └── ssh
│       └── id_syncer.pub
└── docker-compose.yaml

Configuration

Strangely enough, the server side is a lot easier to configure than the client. The container just needs two volumes (one to hold the SSH key, and the other to hold the library content), and one network port on which to listen for incoming rsync-over-SSH connections from the clients.

You can change the port mapping if you'd like, just as long as it's not a port which will be used by the Docker host itself so that incoming connections can be tunneled into the container.

Here's an example docker-compose.yaml for the server:

version: '3'
services:
  library-syncer-server:
    container_name: library-syncer-server
    restart: unless-stopped
    image: ghcr.io/jbowdre/library-syncer-server:latest
    environment:
      - TZ=UTC
    ports:
      - "2222:22"
    volumes:
      - './data/ssh:/home/syncer/.ssh'
      - './data/library:/syncer/library'

Execution

Once everything is in place, start the server:

docker-compose up -d

Client

Preparation

Like the server, the client also needs a ./data/library directory to store the synced templates, but this should be empty to start with.

Be sure to drop the id_syncer private key you generated earlier in ./data/ssh.

If you need to use a custom TLS certificate, place the PEM-formated cert.pem and key.pem in ./data/certs.

Example folder structure:

.
├── data
│   ├── certs
│   │   ├── cert.pem
│   │   └── key.pem
│   ├── library
│   └── ssh
│       └── id_syncer
└── docker-compose.yaml

Configuration

Some decisions need to be made on the client side, and most of those will be expressed in the form of environment variables passed into the container:

Variable	Example value	Description
SYNC_PEER	deb01.lab.bowdre.net	FQDN or IP of the library-syncer server to which the client will connect
SYNC_PORT	2222	SSH port for connecting to the server
SYNC_SCHEDULE	0 21 * * 5	cron-formatted schedule for when the client should initiate a sync (example syncs at 9PM on Friday night)
SYNC_DELAY	true	if true, sleeps a random number of seconds before begining the sync
SYNC_DELAY_MAX_SECONDS	21600	maximum seconds to sleep (example will be delayed up to 6 hours)
TLS_NAME	library.bowdre.net	if set, the FQDN used for the client's web server; if not set, the library will be served strictly over HTTP
TLS_CUSTOM_CERT	true	if true, the web server will expect to find a custom certificate and private key in the ./data/certs volume

Introducing a random sync delay might be useful if you have a bunch of remote sites and don't want them to attempt to sync all at once, but you're too lazy to manually customize the schedule for each one of them (no judgment!).

If you specify a TLS_NAME but don't set TLS_CUSTOM_CERT, the Caddy web server will automatically request and install a Let's Encrypt certificate for your specified FQDN. For this to work, the name must resolve in public DNS, and any firewalls must permit inbound traffic on port 80. Otherwise, the ACME validation will fail and you'll need to go back and try the TLS_CUSTOM_CERT route instead.

Here's a sample docker-compose.yaml for the client:

version: '3'
services:
  library-syncer-client:
    container_name: library-syncer-client
    restart: unless-stopped
    image: ghcr.io/jbowdre/library-syncer-client:latest
    environment:
      - TZ=UTC
      - SYNC_PEER=deb01.lab.bowdre.net
      - SYNC_PORT=2222
      - SYNC_SCHEDULE=0 21 * * 5
      - SYNC_DELAY=true
      - SYNC_DELAY_MAX_SECONDS=21600
      - TLS_NAME=library.lab.bowdre.net
      - TLS_CUSTOM_CERT=true
    ports:
      - "80:80/tcp"
      - "443:443/tcp"
    volumes:
      - './data/ssh:/syncer/.ssh'
      - './data/library:/syncer/library'
      - './data/certs:/etc/caddycerts'

Execution

As before, just bring it up:

docker-compose up -d