Offline store (air-gapped mode)

By default, the Snap Store Proxy operates in online mode. It acts as a smart proxy to the general SaaS Snap Store.

Snap Store Proxy can operate in offline mode and act as a local Snap Store (on-prem store), meaning it can be deployed in networks that are disconnected from the internet.

The intended use case for this mode are network restricted environments where no outside traffic is allowed or possible.

Overview

Client devices connect to the offline store. The local store doesn't directly contact the general SaaS Snap Store nor the internet.

Proxy operators side-load all necessary snaps and other metadata into their local store by exporting them from the SaaS store first and then importing into their offline store.

Brand Store support

Brand Store (also known as IoT App Store) customers can use the Snap Store Proxy in offline mode to securely serve updates to their fleet of devices.

Operators can import their brand store snaps (including any essential and other snaps included from the global store in their brand store) to their on-prem store.

Devices with valid serial assertions for models belonging to a specific brand can authenticate to such on-prem store and get access to imported brand store snaps which are not accessible to any other devices connecting to that on-prem store.

Note: Client devices have to be equipped with their serial assertions.

Installation

If the target host has internet access at the time of installation, then the regular installation and registration can be used followed by airgap mode activation:

sudo snap-proxy enable-airgap-mode

Even though it's possible to enable airgap mode for an online proxy, it's only advised to do so during the installation phase when no devices are yet connected to the proxy. Deactivating and activating airgap mode while it's already serving clients will have undesirable and not clearly defined consequences for the devices that were connected to it before the mode switch as well as for the snap-store-proxy instance itself.

Offline installation

To deploy an offline store (Snap Store Proxy in air-gapped mode) to a machine without internet access it's possible to register it using a separate machine first and install the resulting package on the target machine.

Air-gapped Snap Store Proxy operators first have to register their offline proxy on a machine with internet access. This can be done using the store-admin snap:

sudo snap install store-admin

On the same machine, register the store and obtain a tarball for installation on an offline host (partly pre-configured as well):

# You'll be prompted to authenticate with your Ubuntu SSO authentication.
store-admin register --offline <target-http-location-of-the-store>

Full value of the target location, eg https://snaps.internal, will be encoded in an assertion file used for instructing client devices to connect to this store. It's important to decide if http or https will be used and what the host name will be at the point of registration.

The result of the above is a tarball offline-snap-store.tar.gz that is then moved to the target host machine for the offline store for installation.

The target machine (the air-gapped Snap Store Proxy host) should have network access to a properly configured PostgreSQL database.

You will need the offline-snap-store.tar.gz bundle from the registration step to continue with installation.

The script below illustrates the installation process on the target air-gapped machine. Please note that the following variables need to be set appropriately:

#!/bin/bash

set -eu

# PostgreSQL connection string to the Snap Store Proxy database.
POSTGRESQL_CONN_STRING="${POSTGRESQL_CONN_STRING}"

tar xvzf offline-snap-store.tar.gz
cd offline-snap-store
sudo ./install.sh

sudo snap-store-proxy config proxy.db.connection="$POSTGRESQL_CONN_STRING"

sudo snap-store-proxy enable-airgap-mode

sudo snap-store-proxy status

If the registered store's location was an HTTPS one, follow the HTTPS setup instructions to configure the TLS certificate.

Brand store metadata import

This section is relevant for brand store customers wanting to host their brand store snaps offline and can be skipped if the offline store only has to support Global store client devices (eg. generic devices).

On-prem stores need various data (assertions, snap binaries and metadata, account information) - produced by the upstream Snap Store - to function. This data has to be exported from the SaaS IoT App store and imported into the on-prem store at least once.

Any account keys used for signing brand devices' models and serials have to be registered with the SaaS Snap Store using snapcraft register-key (by the brand account) prior to the export in order for the on-prem store to be able to authenticate brand store devices.

The store export and import steps can be repeated to "synchronise" the data and/or snaps from the SaaS store as needed.

Brand store export

To export brand store metadata needed for import to the on-prem store, the store-admin export store command can be used on a machine with internet access. Authentication using an account with Admin role for the brand store in question is required. Example:

$ store-admin export store \
    --arch=amd64 --arch=arm64 \
    --channel=stable --channel=edge \
    --key=keyId1 --key=keyId2 \
    myDeviceViewStoreID

Logging in as store admin...
Opening an authorization web page in your browser.
If it does not open, please open this URL:
 https://api.jujucharms.com/identity/login?did=idxyz

Downloading store metadata and assertion...
Downloading store admin account details and assertion...
Downloading snap declaration for my-registered-unbpublished-snap1...
Downloading account-key keyId1...
Downloading account-key keyId2...
Downloading core revision 13250 (latest/stable amd64)
  [####################################]  100%
Downloading core revision 13253 (latest/stable arm64)
  [####################################]  100%

...

Creating the export archive...
Store data exported to: /home/ubuntu/snap/store-admin/common/export/store-export-myDeviceViewStoreID-20220527T082652.tar.gz

The above will export the following data:

  • SaaS IoT App Stores' (device view store and its parent) metadata,

  • Registered public keys in form of account-key assertions for key IDs specified with the --key option. Make sure to include the keys used for signing client device serial and model assertions. These keys have to be registered using snapcraft register-key command prior to the export, by the brand account.

  • Snaps available in the SaaS stores, with their metadata and assertions. Currently published revisions of the snaps will be exported according to the specified architectures and channels: --arch, --channel. The --no-snaps option can be used to skip the export of any snap revisions (store-admin export snaps can be used to export snaps in a more granular fashion).

Brand store import

The exported store-export-*.tar.gz file can be imported on the target on-prem host using the snap-proxy push-store command. Example:

sudo snap-proxy push-store \
    /var/snap/snap-store-proxy/common/snaps-to-push/store-export-myDeviceViewStoreID.tar.gz

Side-loading snaps

It's possible to export snaps from the upstream Snap Store and import them into their on-prem store. These will be the only snaps (and their revisions) available for installation from the on-prem store.

Exporting snaps

Example of exporting jq and htop snaps on a machine with internet access using the store-admin snap:

$ store-admin export snaps jq htop --channel=stable --arch=amd64 --arch=arm64 --export-dir .
Downloading jq revision 6 (latest/stable amd64)
  [####################################]  100%
Downloading jq revision 8 (latest/stable arm64)
  [####################################]  100%
Downloading htop revision 3417 (latest/stable amd64)
  [####################################]  100%
Downloading htop revision 3425 (latest/stable arm64)
  [####################################]  100%
Successfully exported snaps:
jq: jq-20221026T104628.tar.gz
htop: htop-20221026T104628.tar.gz

This produces a set of tar.gz files (one per snap name) that have to be moved to the on-prem store host and imported there.

By default snaps are exported from the Global store, and then imported as such, meaning that any device connected to the on-prem store will be able to install them (if it's configured to use the default Global store). store-admin export snaps has a --store option allowing for authenticated export of snaps from private device-view IoT App Stores - after importing these, snaps will be accessible only to properly authenticated devices from the relevant brand.

Importing (pushing) snaps

Once the snap bundles are on the on-prem store host, they should be moved to the /var/snap/snap-store-proxy/common/snaps-to-push/ directory, from where they can be imported.

Example of importing a jq.tar.gz snap bundle on the air-gapped proxy host:

sudo snap-store-proxy push-snap /var/snap/snap-store-proxy/common/snaps-to-push/jq-20200406T103511.tar.gz

The jq snap is now available for installation from this air-gapped Snap Store Proxy. This means that snap info jq and snap install jq will succeed on a connected client device.

Essential snaps

Devices that connect to a store expect that snaps pre-installed on those devices will be available in that store. Otherwise common operations like snap refresh will fail. Air-gapped store operators should ensure that all necessary snaps are imported. Snaps commonly pre-installed on devices may include but are not limited to:

  • core
  • core18
  • core20
  • core22
  • snapd

Status

snap-store-proxy status

lists the imported stores and account keys and

snap-store-proxy list-pushed-snaps

lists all imported snaps.

Running snap info <snap-name> from a device connected to the on-prem store can be used to view more details about the snap, like its current channel map.

Client Device Configuration

Configuring client devices follows the same process as with an online Snap Store Proxy.

Configuration backup

Make sure to securely backup the snap-store-proxy configuration (including the proxy.device-auth.secret used for signing/verifying the device sessions). The config can be exported with:

sudo snap-store-proxy config > proxy-config-backup.txt
sudo snap-store-proxy config proxy.device-auth.secret > proxy.device-auth.secret.txt
sudo snap-store-proxy config proxy.auth.secret > proxy.auth.secret.txt
sudo snap-store-proxy config proxy.key.private > proxy.key.private.txt
sudo snap-store-proxy config proxy.tls.key > proxy.tls.key.txt

Limitations

Offline mode provides only a subset of the core functionality of the online Snap Store Proxy or the SaaS Snap Store. Some of the missing features are:

  • Searching for snaps

  • Generic Device registration. Serial Vault can be used to register custom model devices.