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Draupnir

Draupnir is a tool that provides on-demand Postgres databases with preloaded data.

Odin laid upon the pyre the gold ring called Draupnir; this quality attended it: that every ninth night there fell from it eight gold rings of equal weight.

Development

Prerequisites:

  • Go
  • Postgresql
  • Ruby

Create the database

createdb draupnir

Migrate the database

make migrate

Development (Vagrant VM)

!! Disclaimer, the vagrant VM is currently unsupported on Apple Silicon It will often be desirable to run a full virtual machine, with btrfs, in order to test the complete Draupnir flow. This can be achieved via the included Vagrant configuration.

Install prerequisites:

brew cask install virtualbox vagrant

Build the Linux binary:

make build-linux

Boot Vagrant VM:

vagrant up

Login and use Draupnir:

vagrant ssh
$ sudo su -
# eval $(draupnir new)
# psql -d myapp

After making changes to the code, to restart the server:

make build-linux && vagrant up --provision

Tests

To run the unit tests:

make test

To run the integration tests, ensure you've run make build-linux before running:

make test-integration

Releases

For releases, this project uses GoReleaser. The configuration was done in such a way that releases happen on any commit to the main branch that also updates DRAUPNIR_VERSION, and should be accompanied by an update to CHANGELOG.md to make it explicit what has changed.

Version updates should follow the Semantic Versioning guidelines.

Usage

Draupnir provides an API to create, use and manage instances of your database. There are two API resources: Images and Instances. An Image is a database backup that you upload to Draupnir. Instances are lightweight copies of a particular Image that you can create, use and destroy with ease. We'll walk through the basics of using Draupnir. The full API reference is at the bottom of this document.

Creating an Image

Create a new Image by POSTing to /images, providing a timestamp for the backup and an anonymisation script that will be run against the backup. You can use this to remove any sensitive data from your backup before serving it to users.

POST /images HTTP/1.1
Content-Type: application/json
Draupnir-Version: 1.0.0
Authorization: Bearer 123

{
  "data": {
    "type": "images",
    "attributes": {
      "backed_up_at": "2017-05-01T12:00:00Z",
      "anonymisation_script": "\c my_db\nDELETE FROM secret_tokens;"
    }
  }
}

201 Created
{
  "data": {
    "type": "images",
    "id": 1,
    "attributes": {
      "backed_up_at": "2017-05-01T12:00:00Z",
      "created_at": "2017-05-01T15:00:00Z",
      "updated_at": "2017-05-01T15:00:00Z",
      "ready": false
    }
  }
}

Uploading an Image

Once you've created an Image, you can upload it. This is done by scping a tarball of the database data directory to Draupnir. The upload is authenticated with an ssh key which you'll create when setting up Draupnir.

scp -i key.pem db_backup.tar.gz [email protected]:/draupnir/image_uploads/1

Once you've uploaded the backup, inform Draupnir that you're ready to finalise the image. This may take some time, as Draupnir will spin up Postgres and run the anonymisation script.

POST /images/1/done HTTP/1.1
Content-Type: application/json
Draupnir-Version: 1.0.0
Authorization: Bearer 123

200 OK
{
  ...
}

Creating Instances

Now you've got an image, you can create instances of it. The process for this is very simple.

POST /instances HTTP/1.1
Content-Type: application/json
Draupnir-Version: 1.0.0
Authorization: Bearer 123

{
  "data": {
    "type": "instances",
    "attributes": {
      "image_id": 1
    }
  }
}

201 Created
{
  "data": {
    "type": "instances",
    "id": 1,
    "attributes": {
      "created_at": "2017-05-01T16:00:00Z",
      "updated_at": "2017-05-01T16:00:00Z",
      "image_id": 1,
      "port": "5678"
    }
  }
}

You now have a Postgres server up and running, containing a copy of your database. You can connect to it like you would any other database.

PGHOST=my-draupnir.tld PGPORT=5678 psql my-db

You can make any modifications to this database and they won't affect the original backup. When you're done, just destroy the instance.

DELETE /instances/1
Authorization: Bearer 123
Draupnir-Version: 1.0.0

204 No Content

You can create as many instances of a particular image as you want, without worrying about disk space. Draupnir will only consume disk space for new data that you write to your instances.

Configuration

When draupnir boots it looks for a config file at /etc/draupnir/config.toml. This file must specify all required configuration variables in order for Draupnir to boot. The variables are as follows:

Field Required Description
database_url True A postgresql connection URI for draupnir's internal database.
data_path True The path to draupnir's data directory, where all images and instances will be stored.
environment True The environment. This can be any value, but if it is set to "test", draupnir will use a stubbed authentication client which allows all requests specifying an access token of the-integration-access-token. This is intended for integration tests - don't use it in production. The environment will be included in all log messages.
shared_secret True A hardcoded access token that can be used by automated scripts which can't authenticate via OAuth. At GoCardless we use this to automatically create new images.
trusted_user_email_domain True The domain under which users are considered "trusted". This is draupnir's rudimentary form of authentication: if a user athenticates via OAuth and their email address is under this domain, they will be allowed to use the service. This domain must start with a @, e.g. @gocardless.com.
public_hostname True The hostname that will be set as PGHOST. This is configurable as it may be different to the hostname of the API address that clients communicate with.
sentry_dsn False The DSN for your Sentry project, if you're using Sentry.
clean_interval True The interval at which Draupnir checks and removes any instance associated with a user that no longer has a valid refresh token. Valid values are a sequence of digits followed by a unit, such as "30m", "6h". See time.ParseDuration.
min_instance_port True The minimum port number (inclusive) that may be used when creating a Draupnir instance.
max_instance_port True The maximum port number (exclusive) that may be used when creating a Draupnir instance.
enable_ip_whitelisting False Whether to enable the IP whitelisting module.
whitelist_reconcile_interval False If IP whitelisting is enabled, this is the interval at which Draupnir reconciles the IP address whitelist with what's in iptables, in order to clean up incorrect state. Uses the same format as clean_interval.
use_x_forwarded_for False Whether to use the X-Forwarded-For header when determining the real user IP address. See documentation.
trusted_proxy_cidrs False A list of CIDRs that will match your load balancer IP addresses. Example: ["10.32.0.0/16"]. See documentation.
http.listen_address False The address and port that the HTTPS server will bind to.
http.insecure_listen_address False The address and port that the HTTP server will bind to.
http.tls_certificate False The path to the TLS certificate file that the HTTPS server will use.
http.tls_private_key False The path to the TLS private key that the HTTPS server will use.
oauth.redirect_url True The redirect URL for the OAuth flow.
oauth.client_id True The OAuth client ID.
oauth.client_secret True The OAuth client secret.

For a complete example of this file, see spec/fixtures/config.toml.

CLI

Draupnir ships as a single binary which can be used to run the server or use as a client to manage your instances.

The CLI has built-in help (draupnir help). For help on sub-commands, use an invocation like draupnir images help instead of draupnir help images.

Authenticate

draupnir authenticate

List Images

draupnir images list

Create an instance of Image 3

draupnir instances create 3

Connect to instance 4

eval $(draupnir env 4)
psql

Destroy instance 4

draupnir instances destroy 4

API

The Draupnir API roughly follows the JSON API spec, with a few deviations. The only supported Content-Type is application/json. Authentication is required for most API endpoints and is provided in the form of an access token in the Authorization header.

The API also requires a Draupnir-Version header to be set. This version must be exactly equal to the version of Draupnir serving the API. The CLI and server are distributed as one, and share a version number. We enforce equality here as a conservative measure to ensure that the CLI and API can interoperate seamlessly. In the future we might relax this constraint.

Images

List Images

GET /images HTTP/1.1
Content-Type: application/json
Draupnir-Version: 1.0.0
Authorization: Bearer 123

200 OK
{
  "data": [
    {
      "type": "images",
      "attributes": {
        "backed_up_at": "2017-05-01T12:00:00Z",
        "anonymisation_script": "\c my_db\nDELETE FROM secret_tokens;"
      }
    }
  ]
}

Get Image

GET /images/1 HTTP/1.1
Content-Type: application/json
Draupnir-Version: 1.0.0
Authorization: Bearer 123

200 OK
{
  "data": {
    "type": "images",
    "attributes": {
      "backed_up_at": "2017-05-01T12:00:00Z",
      "anonymisation_script": "\c my_db\nDELETE FROM secret_tokens;"
    }
  }
}

Create Image

POST /images HTTP/1.1
Content-Type: application/json
Draupnir-Version: 1.0.0
Authorization: Bearer 123

{
  "data": {
    "type": "images",
    "attributes": {
      "backed_up_at": "2017-05-01T12:00:00Z",
      "anonymisation_script": "\c my_db\nDELETE FROM secret_tokens;"
    }
  }
}

201 Created
{
  "data": {
    "type": "images",
    "id": 1,
    "attributes": {
      "backed_up_at": "2017-05-01T12:00:00Z",
      "created_at": "2017-05-01T15:00:00Z",
      "updated_at": "2017-05-01T15:00:00Z",
      "ready": false
    }
  }
}

Finalise Image

POST /images/1/done HTTP/1.1
Content-Type: application/json
Draupnir-Version: 1.0.0
Authorization: Bearer 123

200 OK
{
  "data": {
    "type": "images",
    "id": 1,
    "attributes": {
      "backed_up_at": "2017-05-01T12:00:00Z",
      "created_at": "2017-05-01T15:00:00Z",
      "updated_at": "2017-05-01T15:01:00Z",
      "ready": true
    }
  }
}

Destroy Image

DELETE /images/1
Authorization: Bearer 123

204 No Content

Instances

List Instances

GET /instances HTTP/1.1
Content-Type: application/json
Draupnir-Version: 1.0.0
Authorization: Bearer 123

200 Ok
{
  "data": [
    {
      "type": "instances",
      "id": 1,
      "attributes": {
        "created_at": "2017-05-01T16:00:00Z",
        "updated_at": "2017-05-01T16:00:00Z",
        "image_id": 1,
        "port": "5678"
      }
    }
  ]
}

Get Instance

GET /instances HTTP/1.1
Content-Type: application/json
Draupnir-Version: 1.0.0
Authorization: Bearer 123

200 Ok
{
  "data": {
    "type": "instances",
    "id": 1,
    "attributes": {
      "created_at": "2017-05-01T16:00:00Z",
      "updated_at": "2017-05-01T16:00:00Z",
      "image_id": 1,
      "port": "5678"
    }
  }
}

Create Instance

POST /instances HTTP/1.1
Content-Type: application/json
Draupnir-Version: 1.0.0
Authorization: Bearer 123

{
  "data": {
    "type": "instances",
    "attributes": {
      "image_id": 1
    }
  }
}

201 Created
{
  "data": {
    "type": "instances",
    "id": 1,
    "attributes": {
      "created_at": "2017-05-01T16:00:00Z",
      "updated_at": "2017-05-01T16:00:00Z",
      "image_id": 1,
      "port": "5678"
    }
  }
}

Destroy Instance

DELETE /instances/1 HTTP/1.1
Draupnir-Version: 1.0.0
Authorization: Bearer 123

204 No Content

Internal Architecture

Draupnir is basically two things: a manager for BTRFS volumes and a supervisor of PostgreSQL processes. Each image is stored in its own BTRFS subvolume, and instances are created by creating a snapshot of the image's subvolume, and booting a Postgres instance in it. In order to do this, Draupnir requires read-write access to a disk formatted with BTRFS. The path to this disk is specified at runtime by the DRAUPNIR_DATA_PATH environment variable. The whole process looks like this (assuming DRAUPNIR_DATA_PATH=/draupnir):

  1. An image is created via the API (POST /images). This creates a record in Draupnir's internal database and an empty subvolume is created at /draupnir/image_uploads/1 (where 1 is the image ID). The user may specify an anonymisation script to be run on the data before it is made available. At this point, the image is marked as "not ready", meaning it cannot be used to create instances.
  2. A PostgreSQL backup, in the form of a tar file, is pushed into the server over SCP. The ssh credentials for this operation are set when the machine is provisioned, via the chef cookbook. The backup is pushed directly into /draupnir/image_uploads/1.
  3. The image is finalised via the API (POST /images/1/done). This indicates to Draupnir that the backup has completed and no more data needs to be pushed. Draupnir prepares the directory so Postgres will boot from it, and runs the anonymisation script. For more detail on this step see cmd/draupnir-finalise-image. Finally, Draupnir will create a BTRFS snapshot of the subvolume at /draupnir/image_snapshots/1. This snapshot is read-only and ensures that the image will not change from now on. At this point Draupnir marks the image as "ready", meaning that instances can be created from it.
  4. A user creates an instance from this image via the API (POST /instances). First, draupnir creates a corresponding record in its database. Then it will take a further snapshot of the image: /draupnir/image_snapshots/1 -> /draupnir/instances/1 (where 1 is the instance ID). It will start a Postgres process, setting the data directory to /draupnir/instances/1 and binding it to a random port (which we persist in the database as part of the instance).
  5. The instance is now running and can accept external connections (the port range used for instances is exposed via an iptables rule in the cookbook). The user can connect to the instance as if it were any other database, simply by specifying the host (whatever server Draupnir is running on), the port (serialised in the API) and valid user credentials. We expect that the user already knows the credentials for a user in their database, or alternatively they can use the postgres user which we create (with no password) as part of step 3.
  6. The user destroys the instance via the API (DELETE /instances/1). Draupnir stops the Postgres process for that instance and deletes the snapshot /draupnir/instances/1.
  7. The image is destroyed via an API call (DELETE /images). All instances of this image are destroyed as per step 6, and then the image is destroyed by removing the directories /draupnir/image_snapshots/1 and /draupnir/image_uploads/1.

All interaction with BTFS and Postgres is done via a collection of small shell scripts in the cmd directory - read them if you want to know more.

Right now modifications to images (creation, finalisation, deletion) are restricted to a single "upload" user, who authenticates with the API via a shared secret.

Security model

Draupnir has been designed to be deployed on a publicly-accessible instance, but restrict access to the potentially sensitive data in the Draupnir images to authorised users only.

API access

Access to the API is secured via Google OAuth. A user must have a valid token in order to create, retrieve or destroy a Draupnir instance.

Connecting to Draupnir Postgres instances

Access to a Draupnir Postgres instance is secured via a client-authenticated TLS connection. The client certificate and key are served via the API and then stored in a secure temporary location on the client machine. The paths to these files are then used to set PGSSLCERT and PGSSLKEY.

Additionally, PGSSLMODE is set to verify-ca, meaning that the Postgres client will only attempt to connect via TLS, and will also only successfully connect to the instance if it provides the expected CA certificate.

On the server side, when an image is finalised the pg_hba.conf file is setup so that the only method of access is client-authenticated TLS, and this therefore propagates to every instance created from the image. This property ensures that even if a user was to login as a Postgres superuser on their instance and set a blank password for a given database user, then still nobody would be able to connect without a valid client certificate and key.

Each instance has a unique CA, server and client certificate, all generated at creation time, meaning that certificates and keys cannot be reused across instances and that once the instance is created the locally-stored credentials are useless. Given that an instance's details (and therefore credentials) can only be retrieved by the user that created that instance, it also means that only the owning user has access to connect to the instance.

IP address whitelisting

Draupnir provides the ability to dynamically whitelist user IP addresses to further secure the Postgres instances that it creates, protecting them from automated scans and attacks.

This is achieved via iptables rules. If this component is enabled (enable_ip_whitelisting = true in the server config) then the Draupnir daemon will maintain an iptables chain named DRAUPNIR-WHITELIST. It is therefore the administrator's responsibility to provision other iptables rules that reference this chain.

When a user creates an instance, or retrieves the details of one of their own instances, this chain will be populated with a rule that allows new connections to the Postgres instance port, from their IP address only. The rule will be removed as soon as the instance is destroyed.

An example configuration is provided below. This will work in configurations where the default policy of the INPUT chain is ACCEPT. For those with defaults of DROP, the third rule can be omitted.

# In this example, our Draupnir port range is 6432-7432.

# Setup the DRAUPNIR-WHITELIST chain. The server will create this itself if it's
# missing, but we  won't be able to reference the chain unless we do this.
iptables -N DRAUPNIR-WHITELIST

# Allow all connections on the loopback interface
iptables -A INPUT -i lo -p tcp -m tcp --dport 6432:7432 -j ACCEPT

# For any connections which have been successfully opened, allow further
# communication.
iptables -A INPUT -p tcp -m tcp --dport 6432:7432 -m conntrack --ctstate RELATED,ESTABLISHED -j ACCEPT

# For any new connections, pass them through to the DRAUPNIR-WHITELIST chain
iptables -A INPUT -p tcp -m tcp --dport 6432:7432 -m conntrack --ctstate NEW -j DRAUPNIR-WHITELIST

# For any connections that have not been accepted by the whitelist, drop the
# packet
iptables -A INPUT -p tcp -m tcp --dport 6432:7432 -j DROP

The iptables wrapper library used in this project requires root access, and does not support sudo. Because it is strongly recommended to not run the Draupnir server as the root user, this can be worked around by using the provided wrapper script which is installed into the /usr/lib/draupnir/bin directory by the Debian package. The Draupnir server process must be executed with a PATH variable that places this directory at the beginning, in order to ensure it is used instead of the real iptables binary.

Identification of user IP addresses

The Draupnir server creates whitelist rules based on the IP address of the user, which it determines by inspecting the HTTP request that was made to its API.

If your Draupnir API server is fronted by a load balancer, then the HTTP connection that the Draupnir server receives will originate from that, rather than the user directly. In this instance a separate mechanism of determining the user's IP address must be employed; the X-Forwarded-For header.

If this scenario applies to you then the following steps must be taken:

  1. Ensure that your load balancer places the 'real' user IP address in the X-Forwarded-For header.
  2. Enable the use of the X-Forwarded-For header for IP address identification by setting the use_x_forwarded_for variable to true.
  3. Define a list of trusted proxies, via the trusted_proxy_cidrs setting. Any IP addresses in the X-Forwarded-For header that match any of these CIDRs will be ignored. The real user IP address is then determined by taking the resulting list of elements of the X-Forwarded-For header and using the last one (under the assumption that this is the one that your load balancer has added).

If you are not using a load balancer then it is imperative that the use_x_forwarded_for setting remains disabled. If it is enabled without a load balancer present, rewriting the contents of the header, then it's possible for an authenticated user to send API requests with a fabricated X-Forwarded-For header and therefore open up their instance(s) to unauthorized IP addresses.

Cleanup of revoked user instances

When a user creates an instance Draupnir stores the user's refresh token so that it can, at the clean_interval, check that the refresh token is still valid. In the event that the token isn't valid, the instance is deleted. This ensures that instances don't remain available longer than the users have access to Draupnir.

Common causes for an invalid refresh token are:

  • The user has revoked the application's third-party access in the Google account dashboard.
  • The user is suspended via G Suite.
  • The user has been deleted.