Federations with Batch Shipyard
The focus of this article is to explain the federation concept in Batch Shipyard and effectively deploying your workload across multiple pools that may span multiple Azure regions around the world.
In Azure Batch, each pool within a Batch account is considered a logical boundary for related work. Thus jobs and job schedules can only target a single Batch pool for execution. However, it may be desirable to have workloads that span multiple pools as there may be a need for a heterogenous mix of compute nodes types, or the ability to manage a distribution of pools, logically, as a unified resource. Moreover, there should be no restriction for such a logical grouping to be limited to a single Batch account, or even a single region unless data residency, data hydration sensitivity or other requirements prohibit such collections.
To enable multi-pool collections across any number of Batch accounts and regions, Batch Shipyard defines the concept of a federation. Federations are collections of pools that can be provisioned as entirely different configurations but grouped together as a single resource. This enables scenarios such as hybrid VM composition and load balancing workloads by routing jobs to regions where specific capabilities may be available and necessary. Federations also enable rich constraint matching while maintaining important cloud-native features of core Azure Batch such as autoscaling capabilities of the underlying pools.
- Full suite of federation, federated pool and federated job management commands through the CLI
- Simple management of federations through user-defined IDs
- Multi-region support within a single federation
- Ability to dynamically add and remove pools from federations on-demand
- Support for multiple federations simultaneously using a single federation proxy
- Fully automated federation proxy deployment and management including on-demand suspend and restart
- Automatic persisted federation proxy logging to Azure File Storage for diagnostics
- Support for job recurrences (job schedules)
- FIFO ordering of actions within a job or job schedule
- Leverages Azure MSI to eliminate credential passing and backing to a store
- Federation proxies can be run in HA mode
The following picture describes how commands issued through Batch Shipyard affect metadata stores and processing by the federation proxy to ultimately issue Batch service API calls for job scheduling.
Below are some helpful terms that are referenced throughout this guide that are not common to core Azure Batch. It is recommended to review this list before examining the mental model picture.
- Federation: a collection of pools that are logically grouped together.
- Action: a directive for the federation proxy to process. Actions are enqueued on a federation queue.
- Federation proxy: a server which processes actions.
- Federation queue: contains enqueued actions. Actions across multiple jobs or job schedules are not guaranteed to be processed in FIFO order. Actions within a single job or job schedule are guaranteed to be processed in FIFO order.
- Task group: a set of tasks within a job associated with an action.
- Constraint: a condition placed on a job to be applied by the federation proxy when selecting a target pool to schedule to.
- Scheduling slot: Each compute node can contain up to max tasks per node scheduling slots as specified during pool allocation.
- Available scheduling slots: the number of available task scheduling
slots across all compute nodes within a pool that can run a task. The
formula representing this metric is:
(nodes in idle state + nodes in running state) * max tasks per node.
+-------------+ | Azure Files | +------+------+ ^ +----------------------------+ | logging | Federation Metadata in | master | | Azure Storage Blob & Table | election +------------+--------------+ | | <-----------+ Federation Proxy | | +----------+ +----------+ | | +------------+ +--------+ | | | Job | | Pool | | | |Dynamic | |Task | | +----------+ | | Metadata | | Metadata | | | |Resource | |Re-write| | | | push | +----------+ +----------+ | fetch | |Conditioning| |Engine | | | Batch +----------> | +-----------> | +------------+ +--------+ | | Shipyard | +----------------------------+ | +-----------+ +---------+ | | "fed" | | |Constraint | |Service | | | commands | enqueue action +------------------+ dequeue action | |Matching | |Proxy & | | | +---------------> | +----------------> | |Engine | |MSI Auth | | +----------+ | Federation Queue | | +-----------+ +---------+ | | | +---------------------------+ +------------------+ | | schedule | +-----------------------------------------------------------v-------+ | Batch Federation | | +-------------------+ +-------------------+ +-------------------+ | | | Region A | | Region B | | Region C | | | | +------+ +------+ | | +------+ +------+ | | +------+ +------+ | | | | |Pool 0| |Pool 1| | | |Pool 3| |Pool 4| | | |Pool 7| |Pool 8| | | | | +------+ +------+ | | +------+ +------+ | | +------+ +------+ | | | | +------+ | | +------+ +------+ | | | | | | |Pool 2| | | |Pool 5| |Pool 6| | | | | | | +------+ | | +------+ +------+ | | | | | +-------------------+ +-------------------+ +-------------------+ | +-------------------------------------------------------------------+
The following is a brief walkthrough of configuring a Batch Shipyard federation and simple usage commands for creating a federation proxy and submitting actions against federations.
Azure Active Directory Authentication Required
Azure Active Directory authentication is required to create a federation
proxy. When executing the
fed proxy create command, your service
principal must be at least
Owner or a
that does not prohibit the following action along with the ability to
create/read/write resources for the subscription:
This action is required to enable Azure Managed Service Identity on the federation proxy.
The configuration for a Batch Shipyard federation is generally composed of two major parts: the federation proxy and the normal global config, pool, and jobs configuration.
The federation proxy configuration is defined by a federation configuration file.
federation: storage_account_settings: # storage account link name where all # federation metadata is stored # ... other settings proxy_options: polling_interval: federations: # interval in seconds actions: # interval in seconds logging: persistence: # automatically persist logs in real-time to Azure File Storage level: # logging level, defaults to "debug" filename: # filename schema scheduling: after_success: blackout_interval: # scheduling blackout interval for target pool # after success in seconds evaluate_autoscale: # immediately evaluate autoscale after scheduling # success if target pool was autoscale enabled
Please refer to the full federation proxy configuration documentation for more detailed explanations of each option, including other options not shown here.
Special care should be taken with the global configuration while provisioning pools that will take part of a federation. Any task that requires a login for a container registry or a shared data volume must have such configuration applied to all pools within the federation.
If it is known beforehand that a set of container images will be required
for all task groups submitted to the federation, then they should be
specified for all pools that will be part of the federation under
docker_images. Any images that require logins, should
be defined in the credentials configuration.
If task container images will not be known beforehand, then it is imperative
additional_registries contains a list of all
private registry servers required by container images that are referenced by
any task within a task group. The corresponding login information for these
registries should be present in the credentials configuration, including
a private Docker Hub login, if necessary.
Any tasks within task groups referencing
shared_data_volumes should have
pools allocated with the proper
shared_data_volumes before joining the
federation. Special care must be taken here to ensure that any pools that
are in different Batch accounts or regions conform to the same naming
scheme for these volumes used by tasks in task groups.
Federated Job Constraints
Note that none of the
federation_constraints properties are required. They
are provided to allow for specified user requirements and optimizations on
job/task group placement within the federation.
job_specifications: - id: # job id # ... other settings federation_constraints: pool: autoscale: allow: # allow job to be scheduled on an autoscale pool exclusive: # exclusively schedule job on an autoscale pool low_priority_nodes: allow: # allow job to be best-effort scheduled on a pool with low priority nodes exclusive: # best-effort schedule job on a pool with exclusively low priority nodes native: # job must be scheduled on a native container pool windows: # job requires a windows pool location: # job should be routed to a particular Azure region, must be a proper ARM name container_registries: private_docker_hub: # any task in task group with Docker Hub references # refer to a private Docker repository public: - # list of public registries that don't require a login for referenced # container images for all tasks in task group max_active_task_backlog: # limit scheduling a job to pools with queued backlog of tasks ratio: # maximum backlog ratio allowed represented as (active tasks / schedulable slots). autoscale_exempt: # if autoscale pools are exempt from this ratio requirement if there # are no schedulable slots and their allocation state is steady custom_image_arm_id: # job must schedule on a pool with the specified custom image ARM image id virtual_network_arm_id: # job must schedule on a pool with the specified virtual network ARM subnet id compute_node: vm_size: # job must match the named Azure Batch supported Azure VM SKU size exactly cores: amount: # job requires at least this many cores schedulable_variance: # maximum "over-provisioned" core capacity allowed memory: amount: # job requires at least this much memory (allowable suffixes: b, k, m, g, t) schedulable_variance: # maximum "over-provisioned" memory capacity allowed exclusive: # tasks in the task group must run exclusively on the compute node # and cannot potentially be co-scheduled with other running tasks gpu: # job must be scheduled on a compute node with a GPU, # job/task-level requirements override this option infiniband: # job must be scheduled on a compute node with RDMA/IB, # job/task-level requirements override this option tasks: # ... other settings
It is strongly recommended to review the
jobs documentation which contains
more extensive explanations for each
federation_constraints property and
for other general job and task options not shown here.
Important notes on job configuration behavioral modifications due to
- Specifying task dependencies under
depends_onwill result in task ids being modified with a postfix containing a subset of the unique id for federations that do not require unique job ids.
- Container registry credential information should be provided at provisioning
time to all pools that may potentially execute that container on-behalf of
the federation. Please see the
container_registriesconstraint for more information.
- Be mindful of any
input_datathat are specified in the job or corresponding tasks, and if the job should be subject to constraints such as
Federated Pool Configuration
Pools that comprise the federation will have certain configuration options applied to them that will naturally limit which task groups can target them for scheduling within the federation. The following is a non-exhaustive, but perhaps the most important, list of pool options that can affect task group scheduling.
platform_imagewill have a large impact on task group placement routing as task groups can only be scheduled on pools provisioned as their respective configuration of native or non-native. In general, it is recommended to use
nativecontainer pools; however, native container pools may not be appropriate for all situations. Please see this FAQ item for more information on native vs non-native container pools. For maximum federated scheduling efficacy, it is recommended to pick native or non-native and use the same setting consistently across all pools and all job
federation_constraintswithin the federation.
custom_imagewill allow routing of task groups with
vm_sizewill be impacted by
max_tasks_per_nodewill impact available scheduling slots and the
autoscalechanges behavior of scheduling across various constraints.
inter_node_communicationenabled pools will allow tasks that contain multi-instance tasks.
virtual_networkproperties will allow routing of task groups with
This is a non-exhaustive list of potential limitations while using the federation feature in Batch Shipyard.
- All Batch accounts within a federation must reside under the same subscription.
- All task dependencies must be self-contained within the task group.
depends_on_rangebased task dependencies are not allowed, currently.
azure_batchhas restrictions. At the job-level it is not allowed and at the task-level it must be self-contained within the task group. No validation is performed at the task-level to ensure self-containment of input data from other Batch tasks within the task group. Pool-level
azure_batchis not validated.
- A maximum of 14625 actions can be actively queued per unique job id. Actions already processed by the federation proxy do not count towards this limit. This limit only applies to federations that allow non-unique job ids for job submissions.
- Low priority/dedicated compute node constraints are best-effort if scheduled to autoscale-enabled pools that have a mixture of dedicated and low priority nodes. If a task group is scheduled to a pool with dedicated-only nodes due to a specified constraint, but the pool later resizes with low priority nodes, portions of the task group may get scheduled to these nodes.
- Constraints restricting low priority or dedicated execution may be subject to the autoscale formula supplied. It is assumed that an autoscale formula will scale up/down both low priority and dedicated nodes.
- Each pool in a federation should only be associated with one and only one federation. Adding a pool to multiple federations simultaneously will result in undefined behavior.
- Singularity containers are not fully supported in federations.
Ensure that you have sufficient active job/job schedule quota for each Batch account. You may also consider increasing your pool quota if you intend on having many pools within a Batch account that comprise a federation.
Please note that all quotas (except for the number of Batch accounts per region per subscription) apply to each individual Batch account separately. User subscription based Batch accounts share the underlying subscription regional core quotas.
The following will describe many of the federation commands available in
the CLI for managing the federation proxy, federations and action submission.
Federation-related commands are grouped under the
Note that most federation commands have the
--raw option available which
allows callers to consume the result of a command invocation in JSON
Please refer to the usage documentation for a full listing of federation commands and further explanation of each command and options not documented here.
The following list shows a typical set of steps to setup a federation. Please ensure that you've reviewed the prior sections and any relevant configuration documentation before proceeding.
- Construct the
federation.yamlconfiguration file and optionally add a different
storagecredential section link to store federation metadata in a separate region or storage account than that of normal Batch Shipyard metadata.
- Deploy pools that will comprise the federation. These can be autoscale-enabled pools.
- Deploy the federation proxy:
fed proxy create
- Verify proxy:
fed proxy status
- Create a federation:
- With unique job id requirement:
fed create <fed-id>
- Without unique job id requirement:
fed create <fed-id> --no-unique-job-ids
- With unique job id requirement:
- Add pools to the federation:
- With a pool configuration file:
fed pool add <fed-id>
- Without a pool configuration file:
fed pool add <fed-id> --pool-id <pool-id> --batch-service-url <batch-service-url>
- With a pool configuration file:
- Verify federation:
A federation with a unique job id requirement means that all jobs submitted to the federation must have unique job ids. Job submissions which collide with a pre-existing job with the same job id in the federation will be actively rejected. This mode is recommended when federations are shared resources amongst a team. A federation without a unique job id requirement allows jobs to be submitted even if a job with the same id exists in the federation. The federation proxy will attempt to dynamically condition the action such that it can actively co-locate task groups among similarly named jobs. Because this requires specific unique id tracking to disambiguate task groups within the same job on potentially the same target pool, tracking task group submissions can become confusing with a team sharing a federation. This non-unique job id mode is only recommended for a federation with a single user.
Conversly, teardown of a federation would generally follow these steps:
- Ensure all federation jobs have been deleted.
- Destroy the federation proxy:
fed proxy destroy
- Destroy the federation:
fed destroy <fed-id>
If you do not need to destroy the federation, but would like to minimze
the cost of a federation proxy when no jobs will be submitted (e.g., off
work), you can instead suspend the proxy and re-start it at a later time
fed proxy suspend and
fed proxy start commands. In that
case you would not destroy the federation metadata with the
fed destroy <fed-id> command.
Federation jobs have the following commands available:
- Add jobs:
fed jobs add <fed-id>
- List jobs:
fed jobs list <fed-id>
- Terminate jobs:
fed jobs term <fed-id> --job-id <job-id>
- Delete jobs:
fed jobs del <fed-id> --job-id <job-id>
When adding jobs, the specified jobs configuration and pool configuration
(e.g., pool.yaml) are consumed. If specific
overrides are not specified, then the federation job is created with
settings as read from the pool configuration file. It is important
to define job
federation_constraints to override settings read from
the pool configuration, if necessary.
To inspect federation jobs and associated task groups, you can typically follow this pattern:
- Locate the job:
fed jobs list <fed-id> --job-id <job-id>
- Use location info to interact with job/task groups:
- Use Batch Explorer or Azure Portal to graphically manage.
- Directly use Batch Shipyard commands if you have the correct Batch account credentials populated targeting the region with the pool listed in the job location.
Note that listing jobs with the default parameters with
fed jobs list <fed-id> (either with or without scoping the invocation
to a job or job schedule) will only list active job and job schedules tracked
by the federation (and have been submitted to Batch). Meaning, if the action
associated with the job/task group is still enqueued, it will not be listed
with the command. In order to retrieve actions which are enqueued and have
not been processed (or are blocked), you can use the
fed jobs list <fed-id> --job-id <job-id> --queued. This command will list
all queued actions for the specified job id.
Sometimes a job/task group is submitted which can "block" other actions for the same specified job if an improper constraint or other incorrect configuration is specified (this can be particularly acute for non-unique job id federations). You can recover from such issues following these commands:
- Locate the problematic action (unique id) associated with the job/task
group submission, if not known already:
fed jobs list <fed-id> --job-id <job-id> --blocked. This command will also provide a broad reason on why the action was blocked.
- Remove the problematic action (unique id) to unblock processing:
fed jobs zap <fed-id> --unique-id <uid>
Note that there is no recovery after a unique id is removed; the action will need to be re-submitted (with the corrected parameters to prevent the blocking behavior which required the use of prior actions in the first place).