Content
Design guidelines
Design the operation and content of the user interfaces to microservice architecture
Avoid designing a single monolithic User Interface that collects data from many the eHealth microservices into one table or view.
A better option, is to separate different user interfaces and workflows in such a way that there is no need to combine large amounts of data in e.g. the same table view.
Target user interface and workflows to only require data from one (or a few) microservices.
Target the workflows and so that data is only retrieved when they are to be used.
A suggested approach is the use the same microservices strategy to the user interface itself by e.g. introduce micro-apps or micro frontend pattern.
Use of ”Backend for frontend” or API Gateway patterns
API Gateway (or BFF pattern) can be essential, to aggregate multiple downstream calls.
The “API Gateway” pattern can be a useful pattern for the eHealth architectures where there are a small number of backend services.
BFF is a variation of API Gateway pattern and defines a separate API gateway optimized for each kind of client.
Using an API gateway has the following benefits:
Isolate the clients from how the application is partitioned into microservices
Isolated the clients from the problem of determining the locations of service instances
Simplifies the client by moving logic for calling multiple services from the client to API gateway
Reduces the number of requests/roundtrips. For example,
The API gateway enables clients to retrieve data from multiple services with a single round-trip. Fewer requests also means less overhead and improves the user experience.
Translates from a “standard” public web-friendly API protocol to whatever protocols are used internally
…
Read more on the API Gateway and BFF pattern here:
Minimize the amount of data that the backend-for-frontend (BFF) has to calculate on
If the a telemedicine solution or application requires a BFF try to minimize the amount of data that the backend-for-frontend (BFF) has to calculate on
Fetching too much and unnecessary data put an extra load on the BFF, and complicates the BFF.
Minimize the amount of data can by done by:
Target user interface design to microservices (see above Design Guide)
Avoid prefetch of data for e.g. details view in a master-detail pattern
Prefer calling eHealth services directly, only use BFF pattern if really needed
Only do caching in telemedicine solutions or applications if really needed
…
Avoid pre-fetching of data
If you are lucky, you may know enough about what your users will do to next, and thereby be able to prefetch the data they need before it's needed.
Applications (or BFFs) can prefetch the results of a query and placed into the cache
Consider if prefetching is really needed, is the BFF response time better than eHealth services?
Prefetching data may result in the prefetch data is stale, and prefetching too many items increases the load on the eHealth Infrastructure.
Design for concurrency
Design for and recognize other clients may have updated the resources
Automatic updates of the user interface can be used to avoid users looking at and updating old data.
However, automatic updates of the user interface with updated information on the eHealth Infrastructure should be limited.
Auto updates can be done from the client, by periodically requesting same information from the eHealth Infrastructure, leading to
Automatic updates may require unnecessary processing and polling of data.
Automatic updates may put an extra load on the eHealth infrastructure.
Only do auto update of the user interface if really needed.
A ‘better’ option is to recognize other clients may have updated the resources.
A combination of the ETag and If-Match header can prevent one clients update the same resource, and the second overwrites the updates of the first
If the client wishes to request a version aware update, it submits the request with an If-Match header that quotes the ETag from the server:
PUT /Patient/347 HTTP/1.1 If-Match: W/"23"
If the version id given in the If-Match header does not match, the server returns a 412 Precondition Failed status code instead of updating the resource.
Take advantage of the opportunity for caching
Caching are both provided by the eHealth Infrastructure that performs server-side caching, but can also be done in solutions or applications.
See https://ehealth-dk.atlassian.net/wiki/spaces/EDTW/pages/1034354702/Technical+Interactions+with+Services#Caching-on-Searching on caching provided by the infrastructure.
See Client-side caching for recommendations on caching in the telemedicine solutions and applications.
Take advantage of the eHealth Infrastructure Event Model
Infrastructure events can be used in telemedicine solutions or applications to trigger functionality.
The eHealth Infrastructure publish simple events at a CRUD resource level e.g.
patient created,
patient updated,
careplan created,
…
Applications should subscribe to events, instead of polling for changes. Using events is considered more effective than polling for changes.
The events can be used in applications to e.g. update cached information
Make effective use of the user selected contexts
Make effective use of the end user selected context and thereby the results returned by the eHealth services
Use information in context (patient, episode-of-care, careteam ..) as parameter in querying the FHIR services to limit the results.
If e.g., the user has set context (patient, episode-of-care, careteam ..) the context can be used to:
Provide as parameter in querying the FHIR services to limit the results, the eHealth services will then filter and limit the results returned to the client.
E.g., only episode of care relevant to selected care-team
E.g., only tasks relevant to selected care-team
Reduce response times from eHealth services
Minimize data and thereby work in telemedicine solutions or applications.
Reduce the risk of UTH (adverse events, Danish: utilsigtet hændelse)
The context can be considered as three levels of context for Attribute Based Access Control:
Use the care team for searching across resources (avoid Patient and Episode-Of-Care)
Use the patient context for more specific results
The episode-of-care limits the results further. The EOC is often required for updates.
Best practices
NOTICE, example URLs in the following are just examples. Please look at the capability statement in the Implementation Guide for the actual capabilities.
Furthermore, the infrastructure develops and capabilities may change.
Optimize call pattern (call in parallel and do not retrieve data one row at a time)
The eHealth infrastructure effectively support parallel requests. If an Application or BFF needs to request data from different services, prefer parallel calls instead of sequential calls if possible.
However, when calling with many concurrent threads from BFFs, it is may be problematic for the infrastructure (similar to DDoS attacks).
Retrieve data on-demand where possible
Best Practice is to generally retrieve data on-demand where possible
That is, first request data when needed.
Avoid prefetch of data for e.g. details view in a Master-Detail pattern
Avoid caching data with the risk of stale data, cache invalidation issues
Limit the number of context changes to what is necessary
In regards to the Design Guides “Make effective use of the selected context” do this with care.
Changing context comes with a penalty. Selecting or changing context results in the user id, access token etc. is refreshed for the specific security context.
Therefore try to limit the number of context changes.
Use the search APIs' counting options to limit the results to the client
The eHealth infrastructure services supports count, to keep the load on clients, servers and the network minimized.
Count are used to limit the number of resources fetched from the database or server.
Example URL to invoke this method:
GET [base]/Patient?identifier=urn:foo|123&_count=10
See also: http://www.hl7.org/implement/standards/fhir/search.html#count
Take advantage of the opportunity for paging in the Infrastructure
Some of the eHealth services provides support for paging of results.
That is, eHealth API users only need to request to amount of data that is needed, and the limiting of the results can be done at the server or database level.
API users can define a _offset parameter in the request which means that when combined with _count the paging is done on the database level.
Example URL to invoke this method for the first page (assuming page size of 10):
GET [base]/Patient?identifier=urn:foo|123&_count=10&_offset=0
Example URL to invoke this method for the second page:
GET [base]/Patient?identifier=urn:foo|123&_count=10&_offset=10
The eHealth infrastructure has a default page size (i.e., default _count if not given) and maximum page size (i.e., maximum value for the _count parameter).
Apply filtering to searches to get a smaller and more accurate result
Searching for resources is fundamental to the mechanics of FHIR. Generally FHIR use “AND” between the parameters in searching.
Some searches allows for search on multiple ids, instead of multiple gets on each id.
See also:
Use time constraints in searches to get a smaller and more accurate result
A common scenario in searches is to allow searching for resources with values (i.e. timestamps) within a range of dates.
FHIR allows for multiple parameters with the same key, and interprets these as being an AND set. So, for example, a range of &date=gt2022-01-01&date=lt2022-02-01 can be interpreted as any date within January 2022.
Example URL to invoke this method:
GET [base]/Appointment?subject.identifier=7000135&start=gt2022-01-01&start=lt2022-02-01
The search parameter _lastUpdated can be used to select resources based on the last time they were changed:
GET [base]/Appointment?_lastUpdated=gt2022-02-01
This search finds any Appointments changed since 1- February 2022.
Limited support for chained resource references
FHIR allows reference parameters may be "chained"
The eHealth services has limited support for chained resource references.
To save a client from performing a series of search operations, FHIR allows reference parameters may be "chained" by appending them with a period (.). Example:
GET [base]/CarePlan?subject.name=peter
Return all the careplans that have a subject whose name includes "peter“.
However, due to the eHealth microservice architecture and resources are handled by individual microservices, the chained parameters is only possible with the same service. That is, limited to resources handled by same service.