This topic tells you how to benefit from the on-demand service plans for VMware RabbitMQ for Tanzu Application Service.
VMware RabbitMQ for Tanzu Application Service responds to the demands of operators by offering a RabbitMQ on-demand cluster for their app developer teams, in addition to the single-node on-demand plan.
The on-demand cluster plan is designed for workloads that require the same resilience requirements as the pre-provisioned offering, but also require their workloads be isolated. The platform operations team can configure a RabbitMQ for Tanzu Application Service cluster to meet their business requirements and empower app development teams to self-serve their own RabbitMQ cluster.
RabbitMQ for Tanzu Application Service also provides smoke tests for the on-demand plans so that operations teams can validate the app developer workflow for on-demand services. See Smoke Tests.
With the on-demand cluster plan, platform operators can offer their app developers three types of RabbitMQ for Tanzu Application Service service plans:
On-Demand single node—For app developer teams requiring greater isolation than provided by the pre-provisioned approach. App development teams can have full access to their own message broker to adapt the runtime parameters to their requirements. For more information about these parameters, see Parameters and Policies in the RabbitMQ documentation.
On-Demand cluster—For an increased level of message resilience and cluster availability, as well as the benefits of workload isolation mentioned above.
Pre-provisioned—For light to moderate messaging needs, this service is fully operated and managed by platform operators as a service.
For information about the pre-provisioned plan, see Deploying the RabbitMQ for Tanzu Application Service Pre-Provisioned Service. For information about using pre-provisioned plans to isolate workloads, see Creating Isolation with the Tile Replicator.
VMware recommends the on-demand service, which is designed for independent isolated RabbitMQ for Tanzu Application Service service instances. The existing pre-provisioned offering has many RabbitMQ for Tanzu Application Service service instances on a single VM, in a multi-tenancy model. In this multi-tenancy model, a single misbehaving app can take down the entire cluster for everyone.
From research and feedback on the issues customers had when using the pre-provisioned service, VMware is making different design decisions for the on-demand service.
To provide you enough visibility to decide which service to use, the table below describes the current feature discrepancies between the pre-provisioned and on-demand services, and plans for addressing these discrepancies. Please give feedback on how to meet your use case requirements with the on-demand service.
|Enabled in base-64 encoded text box
|Plan to address
|Tier-1 plugins enabled using checkboxes in UI.
|A selection of tier-1 plugins are enabled by default on all instances. Other tier-1 plugins can be optionally enabled by an app developer. See RabbitMQ Server Plugins.
|RabbitMQ admin credentials to access RabbitMQ Management UI
|Can set password using tile UI. For more information, see [Access RabbitMQ Management UI for Pre-Provisioned Service Instances](./managing.html#access-ui-pp).
|Can access by creating a service key, see Create an Admin User for a Service Instance.
|Operator can change. This might cause problems. For more information, see Changing the Erlang Cookie Value Known Issue.
|This is managed by the service. No operator intervention needed.
|RabbitMQ for Tanzu Application Service TLS versions
|Available due to security concerns about the TLS packaged with the pre-provisioned service
|All instances only have TLS v1.1 and TLS v1.2 available.
|Yes. Service instances share resources on the same VM and can affect one another.
|No. On-Demand ensures isolation between service instances by creating a separate VM per service instance.
|External load balancer DNS name
|Disk free alarm limit
|No plans to address. The default persistent disk size is controlled at the plan level and is set relative to memory. This removes the ability to mis-configure the alarm limit.
|Available using HAProxy
|Available using BOSH DNS
|RabbitMQ servers static IP
|Evaluating based on customer needs and feedback
|Policy for new instances
|Plan to address
|Individual instance upgrade
|Possible when using tile replicator
|Plan to address
|Network partition behavior
|TLS enabled between client and RabbitMQ broker, possible to configure peer validation
|TLS between client and the RabbitMQ broker has been implemented.
This plan is designed to be simple to configure, deploy, and use. It gives app developer teams fast access to the power of the leading open source message broker backed by BOSH to meet all but the most demanding high availability app messaging requirements.
This plan can suit high-performance workloads requiring messaging resilience and asynchronous messaging replication. RabbitMQ copies messages to disk for resilience and allows asynchronous messaging replication through the RabbitMQ Federation plugin.
This plan offers:
Like the single node plan, this plan is designed to be simple to configure, deploy and use. It gives app developer teams fast access to the power of the leading Open Source message broker backed by BOSH to meet all but the most demanding high availability app messaging requirements.
This plan can suit high performance workloads requiring messaging resilience (copied to disk) and asynchronous messaging replication through the RabbitMQ Federation plugin. With this plan, however, you also scale out RabbitMQ for Tanzu Application Service to multiple nodes.
This plan offers:
The following are some general principles to be aware of when configuring the cluster plan:
RabbitMQ clustering is not primarily a solution for increased availability. Instead, it is designed for consistency and partition tolerance, as described in the CAP theorem. RabbitMQ clustering provides increased message consistency through queue mirroring. This means that messages accessed in one queue are exactly the same as in another queue. For more information, see Consistency or Availability Tradeoff.
Other options can be used for availability requirements, such as the use of federation between exchanges or queues.
For a detailed description of distributed RabbitMQ brokers, see the RabbitMQ documentation.
Every node in the on-demand cluster maintains a complete database of all metadata, and all changes to the metadata are confirmed by every node in the cluster. Therefore, going beyond seven nodes can have a significant negative impact on performance. For optimum resilience and performance, VMware recommends three nodes for most workloads.
RabbitMQ clusters are only recommended for deployment in low latency networks, which normally means that it is not advisable to deploy these clusters across availability zones (AZs). The stability and performance of the RabbitMQ cluster is heavily influenced by the workload on the nodes, replication choices, and network latency.
For this reason, VMware recommends that you deploy RabbitMQ clusters into a single Ops Manager AZ. However, where different AZs are in the same data center, with reliable low latency links, spanning AZs can be used.
For cloud IaaS deployments, VMware does not recommend that deployments span regions. For example, in Amazon Web Services (AWS) terms, deploying a RabbitMQ cluster across AZs within a region should provide high enough network performance to prevent impacting cluster stability. However, deploying across AWS regions is likely to lead to cluster instability. For more information, see the AWS documentation.
In a distributed messaging system, a tradeoff must be made between availability or consistency when a network partition event occurs and one or more nodes are not able to communicate with each other. The cluster plan lets operators decide how they want the RabbitMQ cluster to react in the event of a network partition.
VMware recommends keeping the default cluster partition option of
pause_minority because this satisfies most use cases. Choosing the
pause_minority partition-handling strategy favors message consistency over availability. For more information about the options for handling partitions, see the RabbitMQ documentation. For a detailed description of the options available in RabbitMQ for Tanzu Application Service, see Clustering and Network Partitions.
Here is an example of how
pause_minority works. If you create a RabbitMQ cluster with three nodes and one node becomes unable to communicate with the other two, this node is in the minority. The node that is in the minority is paused, and the other two nodes continue serving traffic. If each of the nodes loses connectivity with the other two, then the entire cluster is paused to preserve data as no majority can be established. The cluster heals when two or more nodes are able to communicate with each other.
It is important to be aware that message queue availability is different from cluster availability. So, having cluster availability does not mean that all of the messages within the queues are also available.
By default, queues within a RabbitMQ cluster are located on a single node—the node on which they were first declared. However, queues can be configured to mirror across multiple nodes, so that any message published to the queue is replicated to all mirrors. Enabling mirroring can have a negative impact on queue performance because messages must be copied to all mirrors before being acknowledged.
Each mirrored queue consists of one leader replica and one or more mirrors, with the oldest mirror being promoted to the new leader replica if the old leader replica disappears for any reason. Consumers are connected to the leader replica regardless of which node they connect to, and mirrors drop messages that have been acknowledged at the leader replica. Queue mirroring enhances queue availability, but does not distribute load across nodes because each of the participating nodes must still do all the work.
App developers must decide if they want to use queue mirroring and determine the policy they want to apply to their queues. These choices have significant impact on the availability of their queues. For more information, see the RabbitMQ documentation.
Unlike the pre-provisioned plan, the cluster plan does not ship with a default load balancer. Therefore, developers must configure their app to use the array of hosts provided in
VCAP_SERVICES. If developers enable queue mirroring, they must also ensure their apps have re-try logic and reconnection logic that iterates over the range of hosts provided. Most common RabbitMQ clients have this logic built into them. For more information, see the Spring Advanced Message Queuing Protocol (Spring AMQP) documentation.
Because the cluster plan is designed to enable app developer teams to self-serve, not having a load balancer in front of the RabbitMQ cluster has these benefits:
In configuring each plan, there are a number of operational controls that platform operations teams can use to manage the resources consumed by on-demand RabbitMQ:
Control Access—Operators can choose the app development orgs and spaces for which the plans are available and visible. Each plan can be activated or deactivated, and service access and visibility can either be global, or enabled per org and space through the command line.
For example, you might decide to enable the single node on-demand plan across all app developer teams to meet their demand to isolate their workload. You might then choose to offer the on-demand cluster plan only to a subset of app developer teams who require the extra resources.
Set Quotas—You can set a global quota for all on-demand instances that takes precedence over each plan quota. This lets you guard against the risk of over-committing resources, but allows the flexibility of over-committing each plan, so you can meet the fluctuating demands of your app developers.
Control Resource Consumption—Each plan offers more fine-grained control over individual plan resource consumption. At the highest level, you can use the plan quota to control the number of instances that can be deployed within a foundation. For each plan, you can also configure the number of nodes that constitute a cluster (3, 5, or 7), the instance type, and persistent disk storage size to best suit your requirements.
Monitor—You can monitor the number of instances that have been deployed against the quota you have set so that you can plan future resource requirements.
The RabbitMQ for Tanzu Application Service on-demand plans expose a number of configuration options. In most cases, the default configurations meet most app demands. However, it is important for an operations team to consider the options to ensure that they provide the best service to their app developers. This section explains these options.
Note A load balancer, such as HAProxy, is not deployed with on-demand cluster plans.
The following are preconfigured for both the single node and the cluster plans:
RabbitMQ VM Type—When installing using Ops Manager, each RabbitMQ node is configured to have the following properties:
You can change these settings in the Service Plan Configuration page. Changing these settings affects all nodes.
Persistent Disk Type—When installing using Ops Manager, each RabbitMQ node is configured to have 30 GB of persistent disk space.
You can change this setting in the Service Plan Configuration page. VMware recommends you set this value to be twice the amount of RAM of the selected RabbitMQ VM Type.
Metrics—Emitted to the Loggregator Firehose for all on-demand instances. The polling interval is set in Ops Manager, in the Metrics polling interval field, in the Pre-Provisioned RabbitMQ tab of the RabbitMQ for Tanzu Application Service tile. Due to the impact of some of the cluster settings detailed below, VMware strongly recommends that you monitor the exposed metrics and configure alarms as recommended in Monitoring and KPIs for On-Demand VMware RabbitMQ for Tanzu Application Service. See also Monitoring On-Demand RabbitMQ Clusters below.
Logs—On-demand RabbitMQ for Tanzu Application Service service instance logs are forwarded using the same configuration as contained in the Syslog and Metrics tab of the RabbitMQ for Tanzu Application Service tile.
Disk free space limit—The disk free space limit is set to 150% of RAM of the instance type you select. For example, if you select an instance type with 10 GB of RAM, the disk free space limit is set to 15 GB. A cluster-wide alarm is triggered if the amount of free disk space drops below this, and all publishers are blocked. Instances must be configured to have persistent disks that are at least twice the size of instance RAM. For more information, see the RabbitMQ documentation.
Memory threshold for triggering flow control—Threshold at which flow control is triggered is set to 40% of the instance RAM. This means that when the alarm is triggered, all connections publishing messages are blocked cluster-wide until the alarm is cleared.
For example, if you select an instance type with 10 GB of RAM, when more than 4 GB of memory is used, all publishing connections are blocked. For more information, see Memory Alarms in the RabbitMQ documentation.
Memory paging threshold—This is the level at which RabbitMQ tries to free up memory by instructing queues to page their contents out to disk. This is done to try to avoid reaching the high watermark and blocking publishers. This threshold is set to 50% of the configured high watermark, which is 20% of configured memory.
For example, if you select an instance type with 10 GB of RAM, when more than 2 GB of memory is used, all queues start writing all queue contents to disk. For more information, see the RabbitMQ documentation.
It is important to monitor and compare the number of instances that have been deployed against the quota you set using the metric exposed on the Firehose.
Each instance is pre-configured to emit metrics to the Firehose and can be identified by the
deployment tag, which has the service instance ID. It is important to monitor these metrics as recommended in Monitoring and KPIs for On-Demand VMware RabbitMQ for Tanzu Application Service.
VMware recommends the on-demand service for production workloads due to its workload isolation.
For instructions for developers about migrating from a pre-provisioned to an on-demand instance, see Migrating a RabbitMQ for Tanzu Application Service Service Instance to Another Service Instance. For how operators can turn off the pre-provisioned service, see Turning Off the Pre-Provisioned Service.
When migrating from a pre-provisioned to an on-demand offering, be aware of the following:
Pre-provisioned service instances have very low resource consumption, that is, a virtual host within an existing cluster. However, every on-demand service consists of dedicated VMs. Therefore, you must select an on-demand service plan that provides adequate resources, but avoids unnecessary resource consumption.
VMware recommends that you define all required structures in your app to ensure they get defined if you connect to a new instance. These structures include:
If your pre-provisioned instance uses any of the following, ensure that you apply them to the on-demand instance:
There are some differences between pre-provisioned and on-demand services instances that you should be aware of:
On-Demand instances are not fronted by a load balancer, therefore, ensure the following:
The instance you are migrating to might use a different version of RabbitMQ than your old instance. For more information, see the VMware RabbitMQ for Tanzu Application Service Release Notes and the RabbitMQ Changelog.
Critical tier-1 plugins are enabled for on-demand. However, on-demand does not yet have the same plugins enabled as pre-provisioned. If you are missing a plugin, contact your VMware representative.
You might have configured your on-demand instance differently. For example, you might have changed:
If your RabbitMQ for Tanzu Application Service service instance uses TLS, ensure that you enable TLS for on-demand instances. See Enable TLS for Your Service Instance.