policies-pp.html.md.erb

---
breadcrumb: VMware RabbitMQ for Tanzu Application Service Documentation
title: Setting Default Policies for the Pre-Provisioned RabbitMQ Service
owner: London Services
---

<div class="note">
  <strong>Note:</strong> <%= vars.note_pre_provisioned %>
</div>

This topic is about setting default policies for the pre-provisioned RabbitMQ service.
For setting on-demand policies, see
[Setting Default RabbitMQ Policies for the On-Demand Service](policies-od.html).

## <a id="policy"></a> About RabbitMQ Policies

You can set a default queue and an exchange policy in the <%= vars.product_full %> tile to be applied
to the RabbitMQ cluster.
After you deploy the tile, VMware recommends that you use the RabbitMQ Management UI to make
configuration changes.

For more information about RabbitMQ policies, see the
[RabbitMQ documentation](http://www.rabbitmq.com/parameters.html#policies).

To set or change the policy, see the [Set or Change the Policy](#viewing.html) section below.


## <a id="rules"></a> Rules for Policies Set in the Tile

The following rules apply to polices set through the <%= vars.product_short %> tile:

* A new policy, or an update to a policy, only applies to new instances (vhosts).
Existing instances are not affected by the policy.
* The policy can only be deleted manually from the RabbitMQ nodes.
* Policies can be added dynamically using the RabbitMQ Management UI.
* It is not possible to use pattern matching with policies. Policies apply to all queues and exchanges.

    For granular policy settings, VMware recommends using the
    RabbitMQ Management UI. Set a `priority number` lower than
    `50`, the default `priority number` applied through the <%= vars.ops_manager %> configuration.


## <a id="example"></a> An Example Policy: Mirror on Two Nodes

Here is an example policy that ensures messages are mirrored on two nodes:

```
{
  "ha-mode": "exactly",
  "ha-params": 2,
  "ha-sync-mode": "automatic"
}
```

Operators should consider some of the performance implications of making queues and exchanges highly
available.
For more information about highly available queues, see the
[RabbitMQ documentation](https://www.rabbitmq.com/ha.html).


### <a id="syncing_queues"></a>Best Practice for Syncing Queues

When a queue syncs all its messages, they are loaded into memory.
When queues are syncing, they can use as much memory as the total size of all messages.
This applies to both nodes---the node where the queue leader runs (from node)
and the node where the queue follower runs (to node), but only applies to newly created queue
followers.

This behavior is especially relevant when any change affects the deployment,
for example: stemcell updates, deployment configuration changes, and network changes.
Verify that you have enough memory and disk available to support all messages.

For example:

There are 5&nbsp;GB of messages in a mirrored queue that is set to automatic sync.
When this queue needs to sync, the node where the queue leader runs can use up to 5&nbsp;GB of extra
memory. The same applies to the node where the new queue follower is created.


## <a id="viewing"></a> Set or Change the Policy

To set the RabbitMQ policy:

1. From the <%= vars.ops_manager %> Installation Dashboard, click the <%= vars.product_short %> tile
and then click the **Pre-Provisioned RabbitMQ** tab.

1. Under **Deploy Pre-Provisioned service offering**, click **Yes**.

1. Select **Enable custom policy on new instances**.

    <%= image_tag("images/policy_opsman.png",
    :alt => "Screenshot of two fields:
    enabled checkbox field, 'Enable custom policy on new instances, and
    text area field, 'Policy for new instances,' which has the value,
    {'ha-mode':'exactly','ha-params':2,'ha-sync-mode':'automatic'}") %>
1. In the **Policy for new instances** field, paste the policy.

The policy must be valid JSON and should meet valid RabbitMQ policy criteria.

<p class="note">
  <strong>Note:</strong> No policy validation occurs during the deployment, and errors can cause the
  deployment to fail or policies to be applied incorrectly.
</p>


## <a id="dashboard"></a> View Policies in the RabbitMQ Management UI

You can view RabbitMQ policies in the RabbitMQ Management UI, shown below.
The example policy entered in the <%= vars.product_short %> tile above is applied to all queues and
given a **Priority** of **50**.
This allows you to override it by defining another policy with a higher priority.

<%= image_tag("images/policy_config.jpeg",
:alt => "Screenshot of RabbitMQ Management UI. Main header is 'Policies'. An
expanded accordion called 'All Policies' shows a filter text field, a regex checkbox, an a table
with columns titled 'Name', 'Pattern', 'Apply to', 'Definition', and 'Priority'.
One item is in the table with the name 'operator_set_policy' and a Priority of '50'.") %>

In the **Queues** section shown below, you can see that any new queues created have the policy
automatically applied.

<%= image_tag("images/policy_queue.jpeg",
:alt => "Screenshot of RabbitMQ Management UI. Main header is 'Queues'. An
expanded accordion called 'All queues' shows a filter text field, a regex checkbox field, and a table
with one item named 'test'. The policy called 'operator_set_policy' is highlighted in blue in the
'Features' column of the table. The 'state' column shows the item is green and 'running'.") %>

<p class="note">
  <strong>Note:</strong> Developers can obtain the URL of the policy from <code>VCAP_SERVICES</code>
  for app developers.
</p>