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Functional Infrastructural Model

This specification aims to ease service deployment woes in an infrastructure-neutral manner, not complicate them. We acknowledge that IT organizations tend to run services in a combination of:

  • Locally-provisioned, co-located, or managed virtual machines using 3rd-party management tools

  • Bare metal machines and appliances for one-off use cases and legacy needs

  • Cloud IaaS such as Amazon Web Service, Microsoft Azure, and Google Cloud

To make automated Product provisioning possible, all Products MUST meet a set of interoperability criteria prior to being published in a Marketplace that may be validated automatically. The Marketplace API, at the specification level, does not and should not make infrastructure mandates; however, to leverage HL7 Marketplace implementations to the greatest extent, a number of local Platform requirements SHOULD be met. A compatible runtime Platform conceptually unifies three areas of an IT architecture:

  • Packaging - How individual Product Builds are produced by independent software vendors (ISVs) and ultimatel consumed by IT groups.

  • Curation - Definition and announcement of a Product Build’s capabilities and dependencies.

  • Orchestration - Automated service dependency resolution and deployment into local runtime platforms.

What is a "Product"?

The name "Health Services Platform Marketplace" was chosen to imply that a formal definition of a computable artifact, or "Product", is the focal currency of a Marketplace implementation. It is thus necessary to provide criteria for what does/does not constitute a Product in the Service Functional Model (SFM). Products are declared to the Marketplace via a client such as the reference web UI, other compatible application, or script. Each Product instance is primarily a metadata declaration of human-readable fields, and references 0..* "Builds" that in turn point to versioned, executable software images and/or content. These Builds – or most accurately the things they point to – are the meat of what is programmatically bootstrapped into a Platform environment. Product Builds MAY be subject to additional validation and curation per policies defined by the Marketplace operator, based on declared capabilities and content of the marketplace.json file.

Products SHOULD be:

  • SSO Aware using OpenID Connect and/or SAML 2.0. If a service requires user logins, it should be declared as needing an SSO IDP such that configuration can be provided at run-time.

  • Provisionable via IETF SCIM 2 API implementations for individual and batch user and group management. This is a computing standard supported by ActiveDirectory and other identity management systems for synchronization of User and Group records.

  • Profilable supporting OpenTracing-compatible traceability across the architecture independent of programming language, including tracking of context across services boundaries for comprehensive system benchmarking.

  • Incorruptible in the event they are killed without notice.

  • Offline-friendly to environments where no Internet access is permitted, or is subject to significant constraint or disruption.

Products SHOULD NOT be:

  • Bulk data payloads While nothing prevents using a Marketplace for data distribution, service build images are intended to be used for more directly computable assets. (Consider this a guideline that MAY change in the future.) Large data files generally SHOULD NOT be bundled into software images. Rather, container initialization steps should be implemented that download requisite data or pull them from a configured database.

  • Hardware dependent This is software that requires specific physical daughter cards, dongles, GPUs, CPU serial numbers etc. Product runtime Platforms have no presumed means of binding to hardware dependencies. Future extension to image metadata MAY need to make special considerations, however, for frameworks such as OpenCL that aggregate underlying GPU hardware into abstract interfaces. This is currently a matter for future consideration due to differing hardware "passthrough" approaches across environments.

Product Builds and Packaging

We refer to runnable Products as "executable", whereas machine-friendly content requiring some form of external runtime for use is "computable". That is, all executable products are computable, but not all computable products are executable. Executables, due to their OS-dependent nature, have stricter packaging guidelines than simply needing to declare the specific standards with which it complies. These are based on "12 factor" principles.

Executable Product Build images MUST be:

  1. Containerized into a single, OCI-compatible image. Docker Community Edition has been used as the gold standard and runtime verification tool and is recommended, but not required.

  2. Ephemeral. All persistent data must be saved to an external database and declared as a service dependency, if needed.

  3. Injected with configuration All configuration information, including database connection URLs, secret keys, encryption salts, DNS names, base URLs etc MUST be read from runtime environment variables or autodetected according to Twelve Factor principles. ISVs therefore MUST NOT "bake in" files intended to be manually edited by a system administrator, as no such hand editing is guaranteed in a Platform environment. Configuration variable names MUST ONLY be formed from uppercase A-Z, 0-9 numeric, and underscore ‘_’ characters. Values are always strings. (Lowercase is not permitted due to some environments performing configuration resolution using case-insensitive DNS mechanisms.)

  4. Programmatically validates Products declaring standard-compliant capabilities MUST support a mode for exercising declared APIs via a "smoke test" suite that MAY be triggered via a Marketplace itself. Product submissions failing to pass smoke tests on declared capabilities SHOULD be automatically rejected by the operator. Further, ISVs, operators, validators, end users, etc. SHOULD be able to trigger the same smoke test suite if/when they so choose. Operators MAY provide such test harnesses at their discretion. ISV tests specific to a Product or Build SHOULD always be run as an out-of-band activity prior to submission to a Marketplace. Marketplace operators MAY elect to charge ISVs for additional testing and validation procedures at the discretion of the operator.

  5. Horizontally scaled The number of existing containers SHALL be constrained by the Configuration profile submitted by the vendor, at the discretion of the target Platform within defined constraints.

  6. Dynamically scalable Instances are scaled up/down at any time within the limits of the declared Configuration Task minimum/maximum values. Note: For HTTP services, the use of sticky sessions MUST NOT be used, in favor of JWTs or similar lightweight, non-sticky tracking for session state data, when needed.

  7. Single entry process per Configuration profile Task. If a Product Build requires, for example, the image to be run once as a web service and again as a separate worker node, these alternate entry points should be declared as distinct Tasks within the default Configuration at publication time.

  8. Domain name (DNS) agnostic Domain name, SSL/TLS context, and locale-specific settings MUST NOT be hardcoded into a Product Build. Configuration is always either injected at runtime or determined automatically, as can be done with HTTP-based Products.

  9. Unencrypted HTTP Products MUST assume that transport encryption is handled at a separate layer by the runtime Platform. SSL/TLS and reverse proxy load balancing is the responsibility of a target Platform, not the Product Build.

  10. Compute constrained Images must define the maximum per-task RAM requirement at image publication time, and manage use of memory internally to prevent exceeding this boundary. Platforms MUST guarantee that these resources will be available, even if over provisioning virtual environments, and MAY reactively kill Products violating declared constraints.

  11. x86-64. 32-bit binaries are also allowed, but support for other CPU architectures (such as ARM) are optional. This is subject to change.

  12. Self-bootstrapped Every image MUST be able to bootstrap itself into a functional, default state with zero human intervention. This is assumed at publication time and is used for service validation, local consumer evaluation testing, and for seeding production deployments. Products MUST therefore set up any database schema and perform forward migrations automatically without user intervention at deployment, but MAY operate in limited capacity until out-of-band configuration is performed. This is the intended means for activating proprietary licensing schemes.

  13. Stoppable at container shutdown time within 15 seconds. Runtime Platforms are permitted to force kills tasks failing to stop after this timeout period.

  14. Good citizens executing in good faith that they do exactly what they say within the environment (e.g. disclosure of operations being performed, data being stored etc), and do not perform other operations that would not be reasonably expected by a Platform operator or customer.

  15. Traceable Health via process monitoring internal to the container SHOULD include OpenTelemetry client use for the applicable software language/framework.

  16. Logged Products MUST log to standard out/error, and MUST NOT be written to the file system. PHI/PII MAY be logged but SHOULD be toggle-able by the local administrator via injected configuration flags.

What is a compatible "Platform"?

A Health Services Platform is any structured architecture capable of running service containers packaged and distributed according to Marketplace requirements and compatible with the Service Functional Model (SFM). Due to the close relationship between Marketplace functions and Platform capabilities they are two sides of the same fence, though there is no presumption of a standardized "Platform API". While a Platform MAY fully operate without any automated Marketplace integration, and vice versa, doing so limits the potential of automating deployment of knowledge-based (and traditional) services acquired from external parties.

A Marketplace operator's perception of a Platform specification might not a strict specification per se, but a profile of how to use existing technologies in an interoperable way with the ultimate vision of full-stack interoperability and automatability. This stance is necessary since enterprise IT environments already have strategic directions on how core virtualization infrastructure is managed. A prescriptive approach prohibiting deviations would not make traction in existing real-world organizations.

Capabilities

A Platform is fundamentally three things. A(n):

  1. Cluster of servers capable of running arbitrary Product packages according to Marketplace specifications, at minimum.
  2. Orchestration framework of some form for fine-grained management of running services after initial deployment.
  3. Optional agent synchronizing state changes made by 0..N authorized Marketplaces with the target state of the orchestration controller software.

In the exemplar reference implementation discussed in Supplementary Reference Implementation, these capabilities are provided as follows:

  1. A horizontal set of virtual machines running Ubuntu Linux with Docker Community Edition.
  2. Out-of-the-box Docker Swarm with Rancher and Portainer.
  3. A minimalistic proof-of-concept agent listening for changes to the Marketplace-managed target Platform state, capable of initializing new service instances when an event is sent to the local Agent via push notification.

Note that these supplemental materials are NOT part of the specification and are provided for convenience and further information. An example of fictitious on-premise Platform implementation is illustrated in Figure 1, below.

Data Integration Layers

All real-world Platform runtimes require data-level integration with source systems. While necessary in practice, these mechanisms are matters of the Platform operator and are out of scope for this specification.

Example on-premise Platform environment

Example on-premise Platform environment

Note: While reference implementations use Docker, we refrain from using all proprietary features and functions beyond container runtime capabilities. Real-world Platform implementations should choose a mainstream orchestration system if not already present. For Platform environments implemented using cloud resources, Figure 2 illustrates an equally compatible architecture using market-leading Amazon Web Services.

Cloud-based Platform implementation using Amazon Web Services.

Cloud-based Platform implementation using Amazon Web Services