Specification: MicroProfile Health Version: 3.0 Status: Final Release: November 20, 2020
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MicroProfile Health
Rationale
The Eclipse MicroProfile Health specification defines a single container runtime mechanism for validating the availability and status of a MicroProfile implementation. This is primarily intended as a machine to machine (M2M) mechanism for use in containerized environments like cloud providers. Example of existing specifications from those environments include Cloud Foundry Health Checks and Kubernetes Liveness and Readiness Probes.
In this scenario health checks are used to determine if a computing node needs to be discarded (terminated, shutdown) and eventually replaced by another (healthy) instance.
The MicroProfile Health architecture consists of two /health/ready
and /health/live
endpoints in a MicroProfile runtime that respectively represent the readiness and the liveness of the entire runtime.
These endpoints are linked to health check procedures defined with specifications API and annotated respectively with @Liveness
and @Readiness
annotations.
A 3rd endpoint /health
is also available and can be used to provide a combination of the previous endpoints.
These endpoints are expected to be associated with a configurable context, such as a web application deployment, that can be configured with settings such as port, virtual-host, security, etc. Further, MicroProfile Health defines the notion of a procedure that represents the health of a particular subcomponent of an application.
In an application, there can be zero or more procedures bound to a given health endpoint. The overall application health for a given endpoint is the logical AND of all of the procedures bound to it.
The current version of the MicroProfile Health specification does not define how the defined endpoints may be partitioned in the event that the MicroProfile runtime supports deployment of multiple applications. If an implementation wishes to support multiple applications within a MicroProfile runtime, the semantics of individual endpoints are expected to be the logical AND of all the application in the runtime. The exact details of this are deferred to a future version of the MicroProfile Health specification.
Proposed solution
The proposed solution breaks down into two parts:
-
A Java API to implement health check procedures
-
A health checks protocol and wireformat
Contributors
-
John Ament
-
Heiko Braun
-
Clément Escoffier
-
Emily Jiang
-
Werner Keil
-
Jeff Mesnil
-
Andrew Pielage
-
Heiko Rupp
-
Antoine Sabot-Durand
-
Scott Stark
-
Martin Stefanko
-
Kevin Sutter
Java API Usage
Common API check
The main API to provide health check procedures (readiness or liveness) on the application level is the HealthCheck
interface:
@FunctionalInterface
public interface HealthCheck {
HealthCheckResponse call();
}
Applications provide health check procedures (implementation of a HealthCheck
), which will be used by the runtime hosting the application to verify the healthiness of the computing node.
Different kinds of Health Checks
This specification provides different kinds of health check procedures.
Difference between them is only semantic.
The nature of the procedure is defined by annotating the HealthCheck
procedure with a specific annotation.
-
Readiness checks defined with
@Readiness
annotation -
Liveness checks defined with
@Liveness
annotation
A HealthCheck
procedure with none of the above annotations is not an active procedure and should be ignored.
Readiness check
A Health Check for readiness allows third party services to know if the application is ready to process requests or not.
The @Readiness
annotation must be applied on a HealthCheck
implementation to define a readiness check procedure, otherwise, this annotation is ignored.
Liveness check
A Health Check for liveness allows third party services to determine if the application is running. This means that if this procedure fails the application can be discarded (terminated, shutdown).
The @Liveness
annotation must be applied on a HealthCheck
implementation to define a Liveness check procedure, otherwise, this annotation is ignored.
Multiple HealthChecks procedures for a given kind
There can be one or several HealthCheck
exposed for a given kind, they will all be invoked when an inbound protocol request is received (i.e. HTTP).
If more than one HealthCheck
are invoked, they will be called in an unpredictable order.
The runtime will call()
each HealthCheck
which in turn creates a HealthCheckResponse
that signals the health status to a consuming end:
public class HealthCheckResponse {
public enum Status { UP, DOWN }
public abstract String getName();
public abstract Status getStatus();
public abstract Optional<Map<String, Object>> getData();
[...]
}
The status of all HealthCheck
's determines the overall status for the given Health check kind.
Combining multiple kinds of checks
A HealthCheck
implementation may be annotated with multiple kinds of checks.
The procedure will be used to resolve every kind of health check for which it is annotated.
For instance this procedure will be used to resolve liveness and readiness health check.
@Liveness @Readiness public class MyCheck implements HealthCheck { public HealthCheckResponse call() { ... } }
Constructing HealthCheckResponse
's
Application level code is expected to use one of static methods on HealthCheckResponse
to retrieve a HealthCheckResponseBuilder
used to construct a response, i.e. :
public class SuccessfulCheck implements HealthCheck {
@Override
public HealthCheckResponse call() {
return HealthCheckResponse.up("successful-check");
}
}
The name
is used to tell the different checks apart when a human operator looks at the responses.
It may be that one check of several fails and it’s useful to know which one.
It’s required that a response defines a name.
HealthCheckResponse
's also support a free-form information holder, that can be used to supply arbitrary data to the consuming end:
public class CheckDiskspace implements HealthCheck {
@Override
public HealthCheckResponse call() {
return HealthCheckResponse.named("diskspace")
.withData("free", "780mb")
.up()
.build();
}
}
HealthCheckResponse
also provides a constructor to allow instantiation on the consuming end.
Integration with CDI
Any enabled bean with a bean of type org.eclipse.microprofile.health.HealthCheck
and @Liveness
or @Readiness
qualifier can be used as health check procedure.
Contextual references of health check procedures are invoked by runtime when the outermost protocol entry point (i.e. http://HOST:PORT/health
) receives an inbound request
@ApplicationScoped
@Liveness
@Readiness
public class MyCheck implements HealthCheck {
public HealthCheckResponse call() {
[...]
}
}
Health check procedures are CDI beans, therefore, they can also be defined with CDI producers:
@ApplicationScoped
class MyChecks {
@Produces
@Liveness
HealthCheck check1() {
return () -> HealthCheckResponse.named("heap-memory").status(getMemUsage() < 0.9).build();
}
@Produces
@Readiness
HealthCheck check2() {
return () -> HealthCheckResponse.named("cpu-usage").status(getCpuUsage() < 0.9).build();
}
}
Protocol and Wireformat
Abstract
This document defines the protocol to be used by components that need to ensure a compatible wireformat, agreed upon semantics and possible forms of interactions between system components that need to determine the “liveliness” or "readiness" of computing nodes in a bigger system.
Guidelines
Note that the force of these words is modified by the requirement level of the document in which they are used.
-
MUST This word, or the terms "REQUIRED" or "SHALL", mean that the definition is an absolute requirement of the specification.
-
MUST NOT This phrase, or the phrase "SHALL NOT", mean that the definition is an absolute prohibition of the specification.
-
SHOULD This word, or the adjective "RECOMMENDED", mean that there may exist valid reasons in particular circumstances to ignore a particular item, but the full implications must be understood and carefully weighed before choosing a different course.
-
SHOULD NOT This phrase, or the phrase "NOT RECOMMENDED" mean that there may exist valid reasons in particular circumstances when the particular behavior is acceptable or even useful, but the full implications should be understood and the case carefully weighed before implementing any behavior described with this label.
-
MAY – This word, or the adjective “OPTIONAL,” mean that an item is truly discretionary.
Goals
-
MUST be compatibility with well known cloud platforms (i.e. http://kubernetes.io/docs/user-guide/liveness/)
-
MUST be appropriate for machine-to-machine communication
-
SHOULD give enough information for a human administrator
Terms used
Term |
Description |
Producer |
The service/application that is checked |
Consumer |
The probing end, usually a machine, that needs to verify the liveness or readiness of a Producer |
Health Check Procedure |
The code executed to determine the liveliness of a Producer |
Producer status |
The overall status, determined by considering all health check procedure results |
Health check procedure result |
The result of single check |
Protocol Overview
-
Consumer invokes the health check of a Producer through any of the supported protocols
-
Producer enforces security constraints on the invocation (i.e authentication)
-
Producer executes a set of Health check procedures (could be a set with one element)
-
Producer determines the overall status
-
The status is mapped to outermost protocol (i.e. HTTP status codes)
-
The payload is written to the response stream
-
The consumer reads the response
-
The consumer determines the overall status
Protocol Specifics
This section describes the specifics of the HTTP protocol usage.
Interacting with producers
How are the health checks accessed and invoked ? We don’t make any assumptions about this, except for the wire format and protocol.
Protocol Mappings
Health checks (innermost) can and should be mapped to the actual invocation protocol (outermost). This section described some of guidelines and rules for these mappings.
-
Producers MAY support a variety of protocols but the information items in the response payload MUST remain the same.
-
Producers SHOULD define a well known default context to perform checks
-
Each response SHOULD integrate with the outermost protocol whenever it makes sense (i.e. using HTTP status codes to signal the overall status)
-
Inner protocol information items MUST NOT be replaced by outer protocol information items, rather kept redundantly.
-
The inner protocol response MUST be self-contained, that is carrying all information needed to reason about the producer status
Healthcheck Response information
-
The primary information MUST be boolean, it needs to be consumed by other machines. Anything between available/unavailable doesn’t make sense or would increase the complexity on the side of the consumer processing that information.
-
The response information MAY contain an additional information holder
-
Consumers MAY process the additional information holder or simply decide to ignore it
-
The response information MUST contain the boolean
status
of each check -
The response information MUST contain the name of each check
Wireformats
-
Producer MUST support JSON encoded payload with simple UP/DOWN statuses
-
Producers MAY support an additional information holder with key/value pairs to provide further context (i.e. disk.free.space=120mb).
-
The JSON response payload MUST be compatible with the one described in Appendix B
-
The JSON response MUST contain the
name
entry specifying the name of the check, to support protocols that support external identifier (i.e. URI) -
The JSON response MUST contain the
status
entry specifying the status as String: “UP” or “DOWN” -
The JSON MAY support an additional information holder to carry key value pairs that provide additional context
Health Check Procedures
-
A producer MUST support custom, application level health check procedures
-
A producer SHOULD support reasonable out-of-the-box procedures
-
A producer with no liveness procedures expected or installed MUST return positive overall status (i.e. HTTP 200)
-
A producer with no readiness procedures expected or installed MUST return positive overall status (i.e. HTTP 200)
-
A producer with liveness procedures expected but not yet installed MUST return positive overall status (i.e. HTTP 200)
-
A producer with readiness procedures expected but not yet installed MUST return negative overall status (i.e. HTTP 503)
A producer with no procedures expected or installed can be for instance an application server without any deployments (focusing on some different function).
A producer with procedures expected but not yet installed can be for instance a
standalone runtime packaged with the user application, or
an application server with already deployed user applications. User defined health
check procedures thus can be expected but they do not have to be already processed
when the first invocations of /health/*
endpoints are received. See also
the Empty default readiness health check responses section.
Policies to determine the overall status
When multiple procedures are installed all procedures MUST be executed and the overall status needs to be determined.
-
Consumers MUST support a logical conjunction policy to determine the status
-
Consumers MUST use the logical conjunction policy by default to determine the status
-
Consumers MAY support custom policies to determine the status
Empty default readiness health check responses
As readiness determines whether the container may consume requests, the container
is required to return negative overall status
until the user defined readiness checks can be executed. However, in some cases
(e.g. the containers allowing multiple deployments) the container itself may be
required to become ready before user defined readiness procedures can be deployed.
This means that the container cannot know whether some procedures will be expected.
For this reason, users are allowed to specify
MicroProfile Config configuration
value mp.health.default.readiness.empty.response
to UP
to give the container
a hint that it can become ready.
Executing procedures
When executing health check procedures a producer MUST handle any unchecked exceptions and synthesize a substitute respone.
-
The synthesized response MUST contain a
status
entry with a value of "DOWN". -
The synthesized response MUST contain a
name
entry with a value set to the runtime class name of the failing check. -
The synthesized response MAY contain additional information about the failure (i.e. exception message or stack trace)
Disabling default vendor procedures
An implementation is allowed to supply a reasonable default (out-of-the-box) procedures as
defined in the Health Check Procedures section. To disable
all default vendor procedures users can specify a
MicroProfile Config configuration property
mp.health.disable-default-procedures
to true
. This allows the application to process and
display only the user-defined health check procedures.
Security
Aspects regarding the secure access of health check information.
-
A producer MAY support security on all health check invocations (i.e. authentication)
-
A producer MUST NOT enforce security by default, it SHOULD be an opt-in feature (i.e. configuration change)
Appendix A: REST interfaces specifications
Context |
Verb |
Status Code |
Kind of procedure called |
Response |
/health/live |
GET |
200, 500, 503 |
Liveness |
See Appendix B |
/health/ready |
GET |
200, 500, 503 |
Readiness |
See Appendix B |
/health |
GET |
200, 500, 503 |
Liveness + Readiness |
See Appendix B |
Appendix B: JSON payload specification
Response Codes and status mappings
The following table gives valid health check responses for all kinds of health checks:
Request |
HTTP Status |
JSON Payload |
Status |
Comment |
/health/live /health/ready /health |
200 |
Yes |
UP |
Check with payload. See With procedures installed into the runtime. |
/health/live /health/ready /health |
200 |
Yes |
UP |
Check with no procedures expected or installed. See With no procedures expected or installed into the runtime |
/health/live /health/ready /health |
503 |
Yes |
Down |
Check failed |
/health/live /health/ready /health |
503 |
Yes |
Down |
Check with procedures expected but not yet installed. See With procedures expected but not yet installed into the runtime |
/health/live /health/ready /health |
500 |
No |
Undetermined |
Request processing failed (i.e. error in procedure) |
JSON Schema:
{
"$schema": "http://json-schema.org/draft-04/schema#",
"type": "object",
"properties": {
"status": {
"type": "string"
},
"checks": {
"type": "array",
"items": {
"type": "object",
"properties": {
"name": {
"type": "string"
},
"status": {
"type": "string"
},
"data": {
"type": "object",
"patternProperties": {
"[a-zA-Z_]*": {
"type": [
"string",
"boolean",
"number"
]
}
},
"additionalProperties": false
}
},
"required": [
"name",
"status"
]
}
}
},
"required": [
"status",
"checks"
],
"additionalProperties": false
}
(See http://jsonschema.net/#/)
Example response payloads
With procedures installed into the runtime
Status 200
and the following payload:
{
"status": "UP",
"checks": [
{
"name": "myCheck",
"status": "UP",
"data": {
"key": "value",
"foo": "bar"
}
}
]
}
Status 503
and the following payload:
{
"status": "DOWN",
"checks": [
{
"name": "firstCheck",
"status": "DOWN",
"data": {
"key": "value",
"foo": "bar"
}
},
{
"name": "secondCheck",
"status": "UP"
}
]
}
Status 500
{
"status": "DOWN",
"checks": [
{
"name": "example.health.FirstCheck",
"status": "DOWN",
"data": {
"rootCause": "timed out waiting for available connection"
}
},
{
"name": "secondCheck",
"status": "UP"
}
]
}
Architecture
SPI Usage
Implementors of the API are expected to supply implementations of HealthCheckResponse
and HealthCheckResponseBuilder
by providing a HealthCheckResponseProvider
to their implementation. The HealthCheckResponseProvider
is discovered using the default JDK service loader.
A HealthCheckResponseProvider
is used internally to create a HealthCheckResponseBuilder
which is used to construct a HealthCheckResponse
. This pattern allows implementors to extend a HealthCheckResponse
and adapt it to their implementation needs. Common implementation details that fall into this category are invocation and security contexts or anything else required to map a HealthCheckResponse
to the outermost invocation protocol (i.e. HTTP/JSON).
Release Notes
Release Notes for MicroProfile Health 3.0
The following changes occurred in the 3.0 release, compared to 2.2.
A full list of changes may be found on the MicroProfile Health 3.0
Release Notes for MicroProfile Health 2.2
The following changes occurred in the 2.2 release, compared to 2.1
A full list of changes may be found on the MicroProfile Health 2.2
Release Notes for MicroProfile Health 2.1
The following changes occurred in the 2.1 release, compared to 2.0
A full list of changes may be found on the MicroProfile Health 2.1
Release Notes for MicroProfile Health 2.0
The following changes occurred in the 2.0 release, compared to 1.0
A full list of changes may be found on the MicroProfile Health 2.0
API/SPI Changes
-
Deprecation of
@Health
qualifier -
Introduction of
@Liveness
and@Readiness
qualifiers
Protocol and wireformat changes
-
In response JSON format replaced
outcome
andstate
bystatus
. This change breaks backward compatibility with version 1.0 -
Introduction of
/health/live
endpoint that must call all the liveness procedures -
Introduction of
/health/ready
endpoint that must call all the readiness procedures -
For backward compatibility,
/health
endpoint should now call all procedures having@Health
,@Liveness
or@Readiness
qualifiers -
Correction and enhancement of response JSON format.