Overview
The Dead Letter Channel (DLC) is a sub-set of a queue
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, specifically designed to persist messages
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that are typically marked for deletion, providing
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you with a choice on whether to delete, retrieve or reroute the messages from the DLC.
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A DLC queue is created when the first subscription is made for a specific domain (superuser or tenant). By default, the message broker retries a defined number of times
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, when a subscriber does not
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acknowledge a message.
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Once the retry count has been breached
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, the message is removed from the queue
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and placed into the DLC.
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The default number of retries is set to 10, however, this value is configurable.
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For information on how to configure the retry count, see Configuring the Message Retry Count
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.
Functionality Narration
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External publishers/subscribers are not permitted to publish/subscribe to the DLC queue. |
Browsing through the
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DLC Queue
All
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messages that
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have breached the retry count will be dumped into the DLC queue
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. The content of the queue
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can be viewed
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by following the steps below:
- On the main tab in the management console click, Dead Letter Channel - > Browse
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- .
- The DLC browser
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- is displayed in the right side of the pane, as shown below
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- . The message count defines the number of messages in the DLC queue
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- .
- Click Browse under the View column to navigate to each individual message stored in the DLC
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3. The ‘browse’ link would result listing the queue contents as shown in the following,
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The browser would display each message in the DLC along with its message content details
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- . The Destination column shows the name of the
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The user could select one or more messages and perform the operations listed on the top right side corner.
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- original queue.
You can choose to delete, restore or reroute one or more messages.
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Operations in DLC
Delete
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Delete - Permanently delete the message from
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MB.
Restore
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- Re-insert the message
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to the queue
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from which the message
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originated
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.
Reroute
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ReRoute - Allows you to select a destination of choice
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instead of
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restoring the message to the
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original queue. When you click ReRoute, a pop-up menu appears, as shown below
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Once the user selects the queue name he/she desires the message to be re routed to and click on ‘ok’ the message will be placed at the relevant queue.
Functional Aspects
Constraints
Publishing and subscribing to DLC queue would not be permitted for external publishers or subscribers.
DLC queue would be created upon the first subscription made for a specific domain. (superuser or tenant)
The messages would be inserted into the DLC queue when the subscribers do not respond positively and when the retry message count is breached. By default the message retry count would be 10. This is configurable. Which could be found under the section "Message Retry Count Policy"
:
Select the queue name to which the message should be re-routed to and click OK. The message is moved to the relevant queue.
Multitenancy
In order to ensure that
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messages
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can be distinguishable per tenant,
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a
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separate DLC
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is created for every new tenant created. The signature of the DLC queue
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is similar to the
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example below:
{tenant_name}/DeadLetterChannel
The above would ensure This ensures that only the messages exchanged through the queues in a specific tenant domain would be are inserted into the DLC queue.
Configuring the Message Retry Count
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The message retry count could can be configured by following the steps mentioned below, 1) Locate as follows:
- Open the andes-config.xml file located
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- in
$MB_HOME/repository/conf/advanced.
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Locate the
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maximumNumberOfMessageDeliveryAttempts attribute and change the value accordingly. For example,
Code Block language html/xml <maximumNumberOfMessageDeliveryAttempts>15</maximumNumberOfMessageDeliveryAttempts>