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External Server Configuration

Warning

It's recommended that you read through the Configuration Overview page before proceeding with this module.

Configuring the Broker

In the broker section of your app.yaml you will provide all of the necessary settings for Merlin to establish a connection with your broker.

Here, we'll discuss:

Broker Options

Merlin allows for several different broker configurations. This section will detail each of these options and how to configure them. We recommend using RabbitMQ as your broker.

RabbitMQ, AMQPS, and AMQP

See the RabbitMQ Documentation for instructions on how to create a RabbitMQ server.

Once your server is set up, we'll need six keys in the broker section of the app.yaml file:

  1. name: The name of the broker (options are rabbitmq, amqps, or amqp)
  2. username: Username for RabbitMQ user that will be used for accessing the service
  3. password: The path to the file that's storing your RabbitMQ password
  4. server: A URL to the server that you're connecting
  5. port: The port that your server is running on. If left undefined and the name setting is:
    • rabbitmq or amqps the default RabbitMQ TLS port (5671) will be used
    • amqp the default port will be 5672
  6. vhost: The vhost for your RabbitMQ service

Using these settings, Merlin will construct a connection string of the form:

{conn}://{username}:{password}@{server}:{port}/{vhost}

Here conn is amqps (with ssl) when the name field is rabbitmq or amqps, and amqp (without ssl) when the name field is amqp. If you're using a connection option with ssl, see the Security With RabbitMQ section below.

Example

Let's say we create a file in our ~/.merlin/ directory called rabbit.pass. In this file we'll store the password for our RabbitMQ server:

~/.merlin/rabbit.pass
1
my-super-secret-password

Now we'll update the broker section of our app.yaml file to be:

~/.merlin/app.yaml
broker:
    name: rabbitmq
    username: rabbit-username
    password: ~/.merlin/rabbit.pass
    server: server.domain.com
    vhost: rabbit-vhost

The connection string that Merlin generates will then become:

amqps://rabbit-username:my-super-secret-password@server.domain.com:5671/rabbit-vhost
Security With RabbitMQ

Merlin can only be configured to communicate with RabbitMQ over an SSL connection and does not permit use of a RabbitMQ server configured without SSL. Therefore, the default value of the broker_use_ssl celery argument is True for RabbitMQ.

The keys can be given in the broker config as shown below:

broker:
    name: rabbitmq
    username: rabbit-username
    password: ~/.merlin/rabbit.pass
    server: server.domain.com
    vhost: rabbit-vhost

    # ssl security
    keyfile: /var/ssl/private/client-key.pem
    certfile: /var/ssl/amqp-server-cert.pem
    ca_certs: /var/ssl/myca.pem
    # This is optional and can be required, optional or none
    # (required is the default)
    cert_reqs: required

The ssl config with rabbitmq/amqps in the broker is then placed in the broker_use_ssl celery argument.

broker_use_ssl = {
  'keyfile': '/var/ssl/private/client-key.pem',
  'certfile': '/var/ssl/amqp-server-cert.pem',
  'ca_certs': '/var/ssl/myca.pem',
  'cert_reqs': ssl.CERT_REQUIRED
}

Redis and Rediss

Note

If you're using Redis v6.0.0+ and would like to configure with ssl, you'll need to view the Security With Rediss section below after completing this section.

See the Redis Documentation for instructions on how to create a Redis server.

Once your server is set up, we'll need five keys in the broker section of the app.yaml file:

  1. name: The name of the broker (here it will be redis if running without ssl, or rediss if running with ssl)
  2. password: The path to the file that's storing your Redis password
  3. server: A URL to the server that you're connecting
  4. port: The port that your server is running on. Default is 6379.
  5. db_num: The database index (this will likely be 0).

Using these settings, Merlin will construct a connection string of the form:

{name}://:{password}@{server}:{port}/{db_num}

If using ssl, see Security With Rediss for additional setup instructions.

Example

Let's say we create a file in our ~/.merlin/ directory called redis.pass. In this file we'll store the password for our Redis server:

~/.merlin/redis.pass
1
my-super-secret-password

Now we'll update the broker section of our app.yaml file to be:

~/.merlin/app.yaml
broker:
    name: redis
    password: ~/.merlin/redis.pass
    server: server.domain.com
    port: 6379
    db_num: 0

The connection string that Merlin generates will then become:

redis://:my-super-secret-password@server.domain.com:6379/0
Security With Rediss

When using Redis with ssl, aka rediss, (only available with Redis v6.0.0+), there are some additional keys that you'll need to add to your broker section:

broker:
    name: rediss
    password: ~/.merlin/redis.pass
    server: server.domain.com
    port: 6379
    db_num: 0


    # ssl security
    keyfile: /var/ssl/private/client-key.pem
    certfile: /var/ssl/amqp-server-cert.pem
    ca_certs: /var/ssl/myca.pem
    # This is optional and can be required, optional or none
    # (required is the default)
    cert_reqs: required

The ssl config with redis (rediss) in the broker is then placed in the broker_use_ssl celery argument.

broker_use_ssl = {
  'ssl_keyfile': '/var/ssl/private/client-key.pem',
  'ssl_certfile': '/var/ssl/amqp-server-cert.pem',
  'ssl_ca_certs': '/var/ssl/myca.pem',
  'ssl_cert_reqs': ssl.CERT_REQUIRED
}

Redis+Socket

Celery supports Redis connections using Unix domain sockets. For this setup, three keys are required in the broker section:

  1. name: The name of the broker. This will be redis+socket here.
  2. path: The path to the Unix domain socket file for Redis
  3. db_num: The database index

Using these settings, Merlin will construct a connection string of the form:

redis+socket://{path}?virtual_host={db_num}

Example

Let's set the broker configuration to be:

~/.merlin/app.yaml
broker:
    name: redis+socket
    path: /tmp/username/redis.sock
    db_num: 0

The connection string that Merlin generates will then become:

redis+socket:///tmp/username/redis.sock?virtual_host=0

Resolving The Broker Password Field

The broker/password is simply the full path to a file containing your password for the user defined by broker/username.

Example

Say the password to our server is my-super-secret-password. We'd simply take this password, place it in a file, and then link the path to the file in the broker section.

~/.merlin/password-file.pass
1
my-super-secret-password
~/.merlin/app.yaml
broker:
    password: ~/.merlin/password-file.pass

Broker URL

A url option is available to specify the broker connection url, in which case the server name is ignored. The url must include the entire connection url except the ssl if the broker name is recognized by the ssl processing system. Currently the ssl system will only configure the Rabbitmq and Redis servers.

Using the url setting, Merlin will construct a connection string of the form:

{url}

Example

Say we use the default Redis server for our broker:

~/.merlin/app.yaml
broker:
    url: redis://localhost:6379/0

The connection string that Merlin generates will then become:

redis://localhost:6379/0

Configuring the Results Backend

In the results_backend section of your app.yaml you will provide all of the necessary settings for Merlin to establish a connection with your results backend.

Here, we'll discuss:

Results Backend Options

Merlin allows for several different results backend configurations. This section will detail each of these options and how to configure them. We recommend using Redis as your results backend.

Redis and Rediss

Note

If you're using Redis v6.0.0+ and would like to configure with ssl, you'll need to view the Security With Rediss section below after completing this section.

The recommended option to use for your results backend is a Redis server. See the Redis Documentation for instructions on how to create a Redis server.

Once your server is set up, we'll need six keys in the results_backend section of the app.yaml file:

  1. name: The name of the results backend (here it will be redis if running without ssl, or rediss if running with ssl)
  2. password: The path to the file that's storing your Redis password
  3. server: A URL to the server that you're connecting
  4. port: The port that your server is running on. Default is 6379.
  5. db_num: The database index (this will likely be 0).
  6. encryption_key: The path to the encryption key (this is automatically generated by merlin config create)

Using these settings, Merlin will construct a connection string of the form:

{name}://:{password}{server}:{port}/{db_num}

To further understand what the encryption_key is for, see Security With Redis.

If using ssl, see Security With Rediss for additional setup instructions.

Example

Let's say we create a file in our ~/.merlin/ directory called redis.pass. In this file we'll store the password for our Redis server:

~/.merlin/redis.pass
1
my-super-secret-password

Now we'll update the results_backend section of our app.yaml file to be:

~/.merlin/app.yaml
results_backend:
    name: redis
    password: ~/.merlin/redis.pass
    server: server.domain.com
    port: 6379
    db_num: 0
    encryption_key: ~/.merlin/encrypt_data_key

The connection string that Merlin generates will then become:

redis://:my-super-secret-password@server.domain.com:6379/0
Security With Redis

Redis versions less than 6 do not natively support multiple users or SSL. We address security concerns here by redefining the core Celery routine that communicates with redis to encrypt all data it sends to redis and then decrypt anything it receives. Each user should have their own encryption key as defined by results_backend/encryption_key in the app.yaml file. Merlin will generate a key if that key does not yet exist.

Security With Rediss

When using Redis with ssl, aka rediss, (only available with Redis v6.0.0+), there are some additional keys that you'll need to add to your results_backend section:

results_backend:
    name: rediss
    password: ~/.merlin/redis.pass
    server: server.domain.com
    port: 6379
    db_num: 0
    encryption_key: ~/.merlin/encrypt_data_key


    # ssl security
    keyfile: /var/ssl/private/client-key.pem
    certfile: /var/ssl/amqp-server-cert.pem
    ca_certs: /var/ssl/myca.pem
    # This is optional and can be required, optional or none
    # (required is the default)
    cert_reqs: required

The ssl config with redis (rediss) in the results backend is then placed in the redis_backend_use_ssl celery argument.

redis_backend_use_ssl = {
  'ssl_keyfile': '/var/ssl/private/client-key.pem',
  'ssl_certfile': '/var/ssl/amqp-server-cert.pem',
  'ssl_ca_certs': '/var/ssl/myca.pem',
  'ssl_cert_reqs': ssl.CERT_REQUIRED
}

MySQL

Coming soon!

Resolving The Results Backend Password Field

The results_backend/password is interpreted in the following way. First, it is treated as an absolute path to a file containing your backend password. If that path doesn't exist, it then looks for a file of that name under the directory defined under celery/certs. If that file doesn't exist, it then treats results_backend/password as the password itself.

Results Backend URL

A url option is available to specify the results backend connection url, in which case the server name is ignored. The url must include the entire connection url including the ssl configuration.

Using the url setting, Merlin will construct a connection string of the form:

{url}

Example

Say we use the default Redis server for our results backend:

~/.merlin/app.yaml
results_backned:
    url: redis://localhost:6379/0

The connection string that Merlin generates will then become:

redis://localhost:6379/0

The url option can also be used to define a server that is not explicitly handled by the merlin configuration system.

Example

Say we have a PostgreSQL database that we want to connect. We can simply copy/paste the url to the results_backend section:

~/.merlin/app.yaml
results_backend:
    url: db+postgresql://scott:tiger@localhost/mydatabase