Configuration Reference¶
Reference: All application.properties and application.yml configuration keys for Mercury Composable.
At a glance
- What — every
application.properties/application.ymlkey supported by the framework and its optional modules, with type, default, and description.- Why it matters — configuration is how you tune ports, threading, security, and module behavior without touching code.
- For developers and operators configuring and deploying applications.
Mercury Composable applications are configured through application.properties (or the
equivalent application.yml). This page is the exhaustive reference for every configuration
key supported by the framework and its optional modules.
Properties are set in src/main/resources/application.properties and can be overridden via
environment variables or JVM system properties (-Dkey=value) using Spring Boot's standard
property resolution order. When both application.properties and application.yml are
present, .properties takes precedence.
Tip: In
application.yml, dots in property names become nested YAML keys. For example,rest.server.port=8100becomes:
Application Identity¶
application.name¶
| Type | Default |
|---|---|
String |
application |
Human-readable service name shown in the /info actuator response. Falls back to spring.application.name if set.
info.app.version¶
| Type | Default |
|---|---|
String |
— |
Application version string (e.g. 1.2.3) shown in the /info actuator response.
info.app.description¶
| Type | Default |
|---|---|
String |
— |
Application description shown in the /info actuator response.
spring.application.name¶
| Type | Default |
|---|---|
String |
application |
Standard Spring Boot application name; used as a fallback for application.name.
Server¶
api.origin¶
| Type | Default |
|---|---|
String |
* |
Value for the Access-Control-Allow-Origin CORS response header.
hsts.feature¶
| Type | Default |
|---|---|
boolean |
true |
Enable the Strict-Transport-Security response header (HSTS).
oversize.http.response.header¶
| Type | Default |
|---|---|
boolean |
false |
Allow HTTP response headers up to 16 KB (default limit is 8 KB).
rest.server.port¶
| Type | Default |
|---|---|
int |
8085 |
Listening port for the built-in reactive HTTP server.
rest.server.ssl-enabled¶
| Type | Default |
|---|---|
boolean |
false |
Enable TLS on the reactive HTTP server. Requires rest.server.ssl.cert and rest.server.ssl.key.
rest.server.ssl.cert¶
| Type | Default |
|---|---|
String (path) |
— |
Path to a PEM-format X.509 certificate. Use classpath:// or file:// prefix. Required when rest.server.ssl-enabled=true.
rest.server.ssl.key¶
| Type | Default |
|---|---|
String (path) |
— |
Path to a PEM-format private key. Use classpath:// or file:// prefix. Required when rest.server.ssl-enabled=true.
server.port¶
| Type | Default |
|---|---|
int |
8085 |
Fallback listening port used when rest.server.port is not set; also the Tomcat port under Spring Boot.
websocket.binary.size¶
| Type | Default |
|---|---|
int |
(framework default) |
Maximum WebSocket binary message size in bytes.
websocket.idle.timeout¶
| Type | Default |
|---|---|
int |
60 |
WebSocket idle connection timeout in minutes.
websocket.server.port¶
| Type | Default |
|---|---|
int |
(same as rest.server.port) |
Listening port for WebSocket connections. Defaults to rest.server.port.
REST Automation¶
REST Automation enables declarative HTTP endpoint mapping via a YAML configuration file.
Set rest.automation=true and provide a yaml.rest.automation path to activate it. See
REST Automation for the full endpoint configuration syntax.
rest.automation¶
| Type | Default |
|---|---|
boolean |
false |
Enable the REST Automation engine.
spring.mvc.static-path-pattern¶
| Type | Default |
|---|---|
String |
/** |
URL pattern for serving static resources (Spring MVC).
spring.web.resources.static-locations¶
| Type | Default |
|---|---|
String (path) |
— |
Spring Boot alias for static.html.folder; checked as a fallback.
static-content.filter.exclusion¶
| Type | Default |
|---|---|
String (comma-sep) |
— |
URL paths excluded from the static content filter.
static-content.filter.path¶
| Type | Default |
|---|---|
String (comma-sep) |
— |
URL prefixes that the static content filter applies to.
static-content.filter.service¶
| Type | Default |
|---|---|
String |
— |
Route name of a function that pre-processes matching static content requests.
static-content.no-cache-pages¶
| Type | Default |
|---|---|
String (comma-sep) |
— |
URL paths served with Cache-Control: no-cache.
static.html.folder¶
| Type | Default |
|---|---|
String (path) |
classpath:/public |
Location of static web content (HTML, CSS, JS, images).
yaml.rest.automation¶
| Type | Default |
|---|---|
String (comma-sep paths) |
classpath:/rest.yaml |
Location(s) of REST endpoint configuration file(s). Multiple files are merged.
Event Script / Flow Engine¶
Flow configuration files are compiled at startup. Each file lists one or more flow definitions
identified by flow.id. Multiple comma-separated paths are merged. See
Event Script Syntax for the full DSL reference.
max.model.array.size¶
| Type | Default |
|---|---|
int |
1000 |
Maximum array index size for dynamic list variables in event script data models.
yaml.event.over.http¶
| Type | Default |
|---|---|
String (comma-sep paths) |
classpath:/event-over-http.yaml |
Location(s) of the event-over-HTTP target mapping configuration.
yaml.flow.automation¶
| Type | Default |
|---|---|
String (comma-sep paths) |
classpath:/flows.yaml |
Location(s) of Event Script flow definition files.
yaml.journal¶
| Type | Default |
|---|---|
String (comma-sep paths) |
classpath:/journal.yaml |
Location(s) of the journal configuration (lists routes whose messages are recorded).
yaml.multicast¶
| Type | Default |
|---|---|
String (comma-sep paths) |
classpath:/multicast.yaml |
Location(s) of the multicast route configuration. Multicast is a local-JVM fan-out: a message sent to a source route is automatically relayed to all listed target routes within the same in-memory event bus. Format: multicast: [{source: "a.route", targets: ["b.route", "c.route"]}]. Not the same as PostOffice.broadcast(), which is a distributed service-mesh operation.
Component Scanning & Startup¶
modules.autostart¶
| Type | Default |
|---|---|
String (comma-sep or YAML list) |
— |
Route names or flow://<flow-id> identifiers to activate at startup without an inbound request.
spring.component.scan¶
| Type | Default |
|---|---|
String |
— |
Package for Spring Boot component scanning; used alongside web.component.scan when running with rest-spring-3.
web.component.scan¶
| Type | Default |
|---|---|
String (comma-sep packages) |
— |
Java packages to scan for @PreLoad, @MainApplication, @BeforeApplication, and @WebSocketService annotations.
yaml.preload.override¶
| Type | Default |
|---|---|
String (comma-sep paths) |
— |
YAML file(s) that override @PreLoad annotation settings (route name, instance count) without recompiling.
Threading & Performance¶
By default all functions run on Java 21 virtual threads. Use @KernelThreadRunner to pin a
function to the kernel thread pool for blocking-I/O operations that are incompatible with
virtual threads.
deferred.commit.log¶
| Type | Default |
|---|---|
boolean |
false |
Defer write commits in the ElasticQueue overflow buffer. For unit-test use only — do not set in production.
kernel.thread.pool¶
| Type | Default |
|---|---|
int |
100 |
Size of the kernel thread pool for @KernelThreadRunner functions. The framework enforces a minimum of 32; there is no hard maximum, but ~200 is advisory — a JVM can rarely sustain more than ~250 kernel threads.
worker.instances.<route>¶
| Type | Default |
|---|---|
int |
(from @PreLoad) |
Override the concurrency instance count for any named route at startup. Example: worker.instances.my.service=50.
worker.instances.no.op¶
| Type | Default |
|---|---|
int |
500 |
Instance count for the built-in no.op placeholder function.
worker.instances.resilience.handler¶
| Type | Default |
|---|---|
int |
500 |
Instance count for the built-in resilience.handler.
worker.instances.simple.exception.handler¶
| Type | Default |
|---|---|
int |
250 |
Instance count for the built-in simple.exception.handler.
The
worker.instances.<route>pattern accepts any registered route name with dots preserved:worker.instances.v1.get.profile=100.
HTTP Client¶
async.http.temp¶
| Type | Default |
|---|---|
String (path) |
/tmp/async-http-temp |
Temporary folder used to buffer large async HTTP response bodies.
http.client.connection.timeout¶
| Type | Default |
|---|---|
int (ms) |
5000 |
Connection timeout in milliseconds for the built-in async HTTP client.
event.over.http.format¶
| Type | Default |
|---|---|
String |
standard |
Serialization format for outbound Event over HTTP calls: standard
(the language-neutral wire format, interoperable with the
Rust implementation and future ports) or compact (the classic single-character-key
format — a fallback for peers on older versions). Inbound decoding always accepts both
formats automatically, and the /api/event service replies in the requester's format.
Overridable per call (or per target in yaml.event.over.http) with the
x-event-format header.
Distributed Tracing & Observability¶
See the Observability guide for the tracing design and OpenTelemetry/OTLP export; the keys
below tune it. The otel.* keys are read by the opentelemetry-forwarder extension.
log.format¶
| Type | Default |
|---|---|
String |
text |
Application log output format: text (human-readable), compact, or json.
show.application.properties¶
| Type | Default |
|---|---|
String (comma-sep list) |
— |
Application property keys to expose via the /env actuator endpoint.
show.env.variables¶
| Type | Default |
|---|---|
String (comma-sep list) |
— |
Environment variable names to expose via the /env actuator endpoint.
skip.rpc.tracing¶
| Type | Default |
|---|---|
String (comma-sep list) |
async.http.request |
Route names excluded from distributed trace recording.
stack.trace.transport.size¶
| Type | Default |
|---|---|
int |
10 |
Maximum stack-trace lines embedded in an EventEnvelope when an exception occurs.
http.correlation.id.header¶
| Type | Default |
|---|---|
String |
X-Correlation-Id |
HTTP header carrying the business correlation-id (enterprise-specific; case-insensitive on inbound). Captured at the edge and preserved end-to-end — exposed to flows as model.cid and to functions via PostOffice.getMyCorrelationId(). A fresh dash-less UUID is generated when the header is absent. Overridable per endpoint with correlation.id.header in a rest.yaml entry (impedance matching for a legacy caller).
http.trace.id.header¶
| Type | Default |
|---|---|
String |
X-Trace-Id |
HTTP header recognized (inbound, when no W3C traceparent is present) and emitted (outbound by the async HTTP client) as the trace-id. A well-formed traceparent always takes precedence inbound. Overridable per endpoint with trace.id.header in a rest.yaml entry.
kafka.correlation.id.header¶
| Type | Default |
|---|---|
String |
cid |
Kafka message header carrying the business correlation-id (no cross-vendor standard exists for non-HTTP transport, so it is configurable). Read inbound by the Kafka Flow Adapter and written outbound by simple.kafka.notification; a fresh UUID is generated inbound when absent. Overridable per binding with correlation.id.header in a kafka-flow-adapter.yaml entry.
kafka.trace.id.header¶
| Type | Default |
|---|---|
String |
— |
Optional Kafka message header for the trace-id. Inbound: a fallback trace-id source when the upstream sends no W3C traceparent (which always takes precedence). Outbound: simple.kafka.notification stamps the current trace-id under this name alongside traceparent, for legacy downstream consumers. Unset = traceparent-only behavior (unchanged). Overridable per binding with trace.id.header in a kafka-flow-adapter.yaml entry.
kafka.health.timeout¶
| Type | Default |
|---|---|
String (duration) |
5s |
Timeout for the kafka.health probe - a single Kafka Metadata request (KafkaConsumer.listTopics) issued from the module's consumer template; no consumer group, no offsets, no admin privileges. Add kafka.health to mandatory.health.dependencies (or the optional list) to include the cluster in /health.
kafka.health.startup.grace¶
| Type | Default |
|---|---|
String (duration) |
30s |
Start-up grace period for kafka.health: within it the check reports a placeholder healthy status while the Kafka client warms up in the background, so /health never fails or blocks during application start-up. After the first successful probe (or once the grace expires) every check is live and an unreachable cluster fails /health with 503.
otel.trace.forwarder.enabled¶
| Type | Default |
|---|---|
boolean |
true |
Used by the opentelemetry-forwarder extension. false makes the forwarder a no-op (jar present, no export).
otel.exporter.otlp.endpoint¶
| Type | Default |
|---|---|
String |
http://localhost:4318/v1/traces |
OTLP/HTTP traces endpoint the opentelemetry-forwarder extension exports spans to.
otel.exporter.otlp.timeout¶
| Type | Default |
|---|---|
int (ms) |
10000 |
OTLP export timeout for the opentelemetry-forwarder extension.
otel.exporter.otlp.connect.timeout¶
| Type | Default |
|---|---|
int (ms) |
10000 |
TCP/TLS connect timeout for the opentelemetry-forwarder extension's OTLP exporter, separate from the export timeout.
otel.exporter.otlp.compression¶
| Type | Default |
|---|---|
String |
none |
OTLP request-body compression for the opentelemetry-forwarder extension: gzip or none. gzip cuts egress bandwidth for high trace volumes.
otel.service.name¶
| Type | Default |
|---|---|
String |
application.name |
service.name resource attribute the opentelemetry-forwarder extension stamps on every exported span.
otel.exporter.otlp.headers¶
| Type | Default |
|---|---|
String (comma-sep key=value) |
— |
Request headers for the opentelemetry-forwarder extension — where backend API credentials go (e.g. Authorization=Api-Token … for Dynatrace, X-SF-Token=… for Splunk). Source it from the environment with no default — otel.exporter.otlp.headers=${OTEL_EXPORTER_OTLP_HEADERS} — so no secret is hard-coded; unset resolves to no headers.
The
otel.*values support${ENV_VAR:default}substitution, so the forwarder is configured entirely fromapplication.propertieswhile secrets stay in the environment.
Health & Actuators¶
mandatory.health.dependencies¶
| Type | Default |
|---|---|
String (comma-sep list) |
— |
Route names of health-check functions that must all report healthy for /health to return HTTP 200.
optional.health.dependencies¶
| Type | Default |
|---|---|
String (comma-sep list) |
— |
Route names of health-check functions whose failure is reported but does not fail /health.
protect.info.endpoints¶
| Type | Default |
|---|---|
boolean |
false |
When true, the /info, /routes, /lib, and /env endpoints require an X-App-Instance header.
Spring Boot Integration¶
These properties are relevant only when using the rest-spring-3 module.
spring.boot.main¶
| Type | Default |
|---|---|
String |
org.platformlambda.rest.RestServer |
Main class for the Spring Boot application. Override to use a custom entry point.
spring.profiles.active¶
| Type | Default |
|---|---|
String (comma-sep list) |
— |
Active Spring profiles; enables profile-specific config files (e.g. application-prod.properties).
Service Mesh / Cloud Connector¶
The service mesh is provided by the optional connectors modules. Set cloud.connector=kafka
to enable inter-instance routing through Kafka. See Minimalist Service Mesh
for a setup walkthrough.
Core Connector¶
application.feature.route.substitution¶
| Type | Default |
|---|---|
boolean |
false |
Enable the route substitution feature to redirect one route name to another at runtime.
cloud.client.properties¶
| Type | Default |
|---|---|
String (comma-sep paths) |
file:/tmp/config/kafka.properties, classpath:/kafka.properties |
Location(s) of the Kafka client properties file.
cloud.connector¶
| Type | Default |
|---|---|
String |
none |
Cloud connector type. none disables the service mesh; kafka enables the Kafka connector.
cloud.services¶
| Type | Default |
|---|---|
String (comma-sep list) |
— |
Additional cloud services to register at startup.
route.substitution¶
| Type | Default |
|---|---|
String (comma-sep a:b pairs) |
— |
Inline route substitutions where b replaces a. Example: old.route:new.route.
user.cloud.client.properties¶
| Type | Default |
|---|---|
String (comma-sep paths) |
file:/tmp/config/second-kafka.properties, classpath:/second-kafka.properties |
Location(s) of a second Kafka client properties file for dual-cluster deployments.
yaml.route.substitution¶
| Type | Default |
|---|---|
String (comma-sep paths) |
— |
YAML file(s) defining route substitution mappings.
Kafka Topic Management¶
app.partitions.per.topic¶
| Type | Default |
|---|---|
int |
32 |
Maximum Kafka partitions per application topic.
app.topic.prefix¶
| Type | Default |
|---|---|
String |
multiplex |
Prefix for auto-generated application Kafka topics.
application.feature.topic.substitution¶
| Type | Default |
|---|---|
boolean |
false |
Enable topic substitution for pre-allocated Kafka topics.
closed.user.group¶
| Type | Default |
|---|---|
int |
1 |
Closed user group number for this instance (must be between 1 and max.closed.user.groups).
default.app.group.id¶
| Type | Default |
|---|---|
String |
appGroup |
Default Kafka consumer group ID for application instances.
default.monitor.group.id¶
| Type | Default |
|---|---|
String |
monitorGroup |
Kafka consumer group ID for presence monitor instances.
kafka.replication.factor¶
| Type | Default |
|---|---|
int |
3 |
Replication factor for auto-created Kafka topics.
max.closed.user.groups¶
| Type | Default |
|---|---|
int |
10 |
Number of closed user groups (range 3–30).
max.virtual.topics¶
| Type | Default |
|---|---|
int |
288 |
Maximum number of virtual topics (= partitions × topic count).
monitor.topic¶
| Type | Default |
|---|---|
String |
service.monitor |
Kafka topic name for presence monitoring signals.
presence.properties¶
| Type | Default |
|---|---|
String (comma-sep paths) |
file:/tmp/config/presence.properties, classpath:/presence.properties |
Kafka connection properties for the presence monitor.
service.monitor¶
| Type | Default |
|---|---|
boolean |
false |
When true, this instance acts as a presence monitor rather than a regular service node.
yaml.topic.substitution¶
| Type | Default |
|---|---|
String (comma-sep paths) |
file:/tmp/config/topic-substitution.yaml, classpath:/topic-substitution.yaml |
YAML file(s) defining topic substitution mappings.
Scheduler¶
These properties are used by the optional mini-scheduler module.
deferred.start¶
| Type | Default |
|---|---|
boolean |
false |
Defer scheduler startup until triggered manually, e.g. to wait for leader election.
leader.election¶
| Type | Default |
|---|---|
boolean |
false |
Enable leader election so that only one instance in a cluster runs each scheduled job.
yaml.cron¶
| Type | Default |
|---|---|
String (comma-sep paths) |
file:/tmp/config/cron.yaml, classpath:/cron.yaml |
Location(s) of the cron job definition file(s). Multiple files are merged.
PostgreSQL (reactive-postgres extension)¶
These properties configure the optional reactive-postgres extension. postgres.host,
postgres.port, postgres.user, and postgres.password are required when the extension
is on the classpath.
logging.level.io.r2dbc.postgresql.PARAM¶
| Type | Default |
|---|---|
String |
— |
R2DBC parameter logging level (e.g. DEBUG). Never set in production — exposes parameter values and may leak PII.
logging.level.io.r2dbc.postgresql.QUERY¶
| Type | Default |
|---|---|
String |
— |
R2DBC query logging level (e.g. DEBUG). Never set in production — exposes SQL queries.
postgres.connection.pool¶
| Type | Default |
|---|---|
int |
20 |
R2DBC connection pool size (minimum 5).
postgres.database¶
| Type | Default |
|---|---|
String |
postgres |
PostgreSQL database name.
postgres.host¶
| Type | Default |
|---|---|
String |
— |
PostgreSQL server hostname or IP. Required.
postgres.password¶
| Type | Default |
|---|---|
String |
— |
PostgreSQL password. Required. Supports ${ENV_VAR} substitution.
postgres.port¶
| Type | Default |
|---|---|
int |
— |
PostgreSQL server port. Required.
postgres.repository.scan¶
| Type | Default |
|---|---|
String |
— |
Java package(s) to scan for Spring Data R2DBC repositories. Required.
postgres.ssl¶
| Type | Default |
|---|---|
boolean |
true |
Enable SSL/TLS for the PostgreSQL connection.
postgres.user¶
| Type | Default |
|---|---|
String |
— |
PostgreSQL username. Required. Supports ${ENV_VAR} substitution.
Minimalist Kafka library¶
The opt-in minimalist-kafka library routes Kafka topics into Event Script flows and publishes events to
Kafka. See the Kafka Flow Adapter guide. The inbound adapter starts only when
yaml.kafka.flow.adapter is set; the outbound simple.kafka.notification function registers automatically.
yaml.kafka.flow.adapter¶
| Type | Default |
|---|---|
String (path) |
— |
Location of the kafka-flow-adapter.yaml binding file (topic -> flow). Unset = inbound adapter disabled.
kafka.producer.properties¶
| Type | Default |
|---|---|
String (path, or comma-sep fallback list) |
classpath:/kafka-producer.properties |
Producer client config template location. Externalization of configuration is opt-in: point this at a file rendered by the devops pipeline (e.g. file:/tmp/config/kafka-producer.properties), optionally with a classpath fallback.
kafka.consumer.properties¶
| Type | Default |
|---|---|
String (path, or comma-sep fallback list) |
classpath:/kafka-consumer.properties |
Consumer client config template location. Externalize the same way as the producer template.
kafka.dlq.timeout.ms¶
| Type | Default |
|---|---|
long (ms) |
10000 |
Confirm-write timeout for the dead-letter publish (broker ack). Flow processing has no timeout knob — the flow's own ttl is the deadline (Kafka is asynchronous).
kafka.flow.max.retries¶
| Type | Default |
|---|---|
int |
3 |
Retry attempts on a flow-processing failure before dead-lettering.
kafka.flow.retry.backoff.ms¶
| Type | Default |
|---|---|
long (ms) |
500 |
Pause between retry attempts.
schema.registry.url¶
| Type | Default |
|---|---|
String (URL) |
— |
Confluent Schema Registry URL. Unset = schema features off (raw byte[]); set to enable the Schema Registry integration (JSON Schema / Avro — Protobuf is not currently supported).
schema.registry.properties¶
| Type | Default |
|---|---|
String (comma-sep paths) |
classpath:/schema-registry.properties |
Registry client template location; externalize the same way as the producer template. Entries pass verbatim to the Confluent client — authentication (bearer.auth.* OAuth 2.0, basic auth) and SSL. OAuth token endpoint URLs found in a template are auto-registered on the JVM org.apache.kafka.sasl.oauthbearer.allowed.urls allow-list.
schema.registry.cache.ttl¶
| Type | Default |
|---|---|
| duration | 30m |
Time-to-live for an entry in the in-memory (platform ManagedCache) cache of schemas fetched by id. Positive results only — a not-found id is never cached, so a newly-registered schema is visible immediately. The TTL bounds how long a cached schema is reused before re-fetching; 30m lets schema changes be picked up without a pod restart (lengthen it in production where schemas change rarely). Cleared at startup (rebuildable).
yaml.secondary.kafka.flow.adapter¶
| Type | Default |
|---|---|
String (location) |
— |
twin-kafka: secondary-cluster adapter config location; unset = secondary inbound adapter off.
secondary.kafka.producer.properties / secondary.kafka.consumer.properties¶
| Type | Default |
|---|---|
String (path, or comma-sep fallback list) |
classpath:/secondary-kafka-*.properties |
twin-kafka: secondary-cluster client template location; same mechanics as the primary templates.
secondary.schema.registry.url / secondary.schema.registry.properties¶
| Type | Default |
|---|---|
String |
— |
twin-kafka: the secondary cluster's own optional Schema Registry (URL = feature switch; template passed verbatim to the Confluent client). Registries and their schema-id caches are per-cluster.
secondary.kafka.health.timeout / secondary.kafka.health.startup.grace¶
| Type | Default |
|---|---|
String (duration) |
fall back to the kafka.health.* globals |
twin-kafka: tunables for secondary.kafka.health, the secondary cluster's twin of kafka.health. A bridge lists both: mandatory.health.dependencies=kafka.health, secondary.kafka.health.
secondary.kafka.correlation.id.header / secondary.kafka.trace.id.header¶
| Type | Default |
|---|---|
String |
fall back to the kafka.* globals |
twin-kafka: outbound header names on the secondary cluster when the two clusters follow different conventions.
The Kafka connection and security settings (bootstrap.servers, security.protocol, sasl.*, ssl.*,
acks, auto.offset.reset) live in the kafka-producer.properties / kafka-consumer.properties template
files — not as application.properties keys — so any enterprise installation is configured by editing or
overriding those templates. All template values support ${ENV_VAR:default} substitution; bootstrap.servers
defaults to ${KAFKA_BOOTSTRAP_SERVERS:127.0.0.1:9092}. The library pins the (de)serializers; the consumer's
enable.auto.commit / max.poll.records are a per-binding overlay (see auto-commit below), not a global
template setting.
Per-binding fields in kafka-flow-adapter.yaml (all ${ENV_VAR:default}-substitutable): exactly one of
topic (literal) or topic-pattern (regex, subscribed via subscribe(Pattern)) is required; flow
(required); group (optional consumer group, used verbatim; default kafka-flow-adapter.<topic> for a
literal topic, required for topic-pattern); partition (optional; pins one partition via manual
assignment, mutually exclusive with topic-pattern); schema.enabled (optional boolean, default false;
when true, decode the Confluent-framed value to a Map before routing — see the
Schema Registry integration); dlq-topic (optional; pre-provisioned
dead-letter topic for this binding, used verbatim — no DLQ if omitted); auto-commit (optional boolean,
default false; true uses Kafka-native auto-commit instead of manual commit-after-process); and
max-poll-records (optional int; overrides the delivery mode's default of 1 for manual-commit or 500
for auto-commit). See the Kafka Flow Adapter guide for the full
per-field rationale and validation rules.
Sync-over-Async (sync-over-async extension)¶
The opt-in sync-over-async extension exposes a synchronous REST request/response over an asynchronous,
cross-pod Kafka backend using a Redis return route. See the Sync-over-Async guide. It is
off by default and starts (eagerly connecting to Redis) only when sync.over.async.enabled=true.
sync.over.async.enabled¶
| Type | Default |
|---|---|
boolean |
false |
Master switch. true starts the Redis return-route coordinator at boot.
redis.host¶
| Type | Default |
|---|---|
String |
127.0.0.1 |
Redis host.
redis.port¶
| Type | Default |
|---|---|
int |
6379 |
Redis port.
redis.password¶
| Type | Default |
|---|---|
String |
— (blank) |
Auth password; blank = no auth. Source from the environment (${REDIS_PASSWORD}).
redis.ssl¶
| Type | Default |
|---|---|
boolean |
false |
Use TLS (rediss://).
redis.database¶
| Type | Default |
|---|---|
int |
0 |
Logical Redis database index.
redis.timeout.ms¶
| Type | Default |
|---|---|
long (ms) |
5000 |
Default Redis command timeout.
sync.return.channel.prefix¶
| Type | Default |
|---|---|
String |
svc-return |
Prefix for the per-pod Pub/Sub return channel.
sync.route.ttl.seconds¶
| Type | Default |
|---|---|
long (s) |
90 |
TTL for the return-route key; should cover the REST timeout plus a buffer.
sync.response.ttl.seconds¶
| Type | Default |
|---|---|
long (s) |
30 |
TTL for the response key (short rendezvous window).
sync.max.pending.requests¶
| Type | Default |
|---|---|
int |
10000 |
Per-pod ceiling on in-flight synchronous requests (backpressure).
All redis.* and sync.* values support ${ENV_VAR:default} substitution.
Serialization & Content Types¶
custom.content.types¶
| Type | Default |
|---|---|
String (comma-sep list) |
— |
Content-type resolver rules in vendor-type -> canonical-type format. Example: application/vnd.acme+json -> application/json.
mime.types¶
| Type | Default |
|---|---|
| Map (YAML only) | — |
Map of file extension to MIME type. Example: mime.types.svg: image/svg+xml.
snake.case.serialization¶
| Type | Default |
|---|---|
boolean |
false |
When true, JSON output uses snake_case field names instead of camelCase.
Data Storage¶
running.in.cloud¶
| Type | Default |
|---|---|
boolean |
false |
When false, a per-instance subdirectory is created under transient.data.store. When true, the path is used as-is (for ephemeral containers).
transient.data.store¶
| Type | Default |
|---|---|
String (path) |
/tmp/reactive |
Base directory for the ElasticQueue overflow buffer that absorbs event bursts when consumers are slower than producers.
Complete Example¶
A typical src/main/resources/application.properties for a REST-serving composable
application. This covers the properties most developers will need to configure.
#
# Mercury Composable — Example application.properties
#
# --- Application Identity ---
application.name=my-service
info.app.version=1.0.0
info.app.description=My composable microservice
# --- Server ---
rest.server.port=8100
# --- REST Automation ---
rest.automation=true
yaml.rest.automation=classpath:/rest.yaml
static.html.folder=classpath:/public
# --- Event Script / Flows ---
yaml.flow.automation=classpath:/flows.yaml
# --- Component Scanning ---
web.component.scan=com.example.myapp
# --- Threading ---
# Increase only if many @KernelThreadRunner functions are used.
kernel.thread.pool=100
# --- HTTP Client ---
http.client.connection.timeout=5000
# --- Distributed Tracing ---
# The trace ID travels as the "X-Trace-Id" header and the W3C "traceparent" header (traceId + spanId).
# Both are emitted outbound and accepted inbound; "traceparent" takes precedence on inbound. No config.
# --- Correlation ID ---
# Business correlation-id headers (configurable; defaults shown). Captured at the edge, preserved as
# model.cid, and propagated downstream. A fresh UUID is generated when absent.
http.correlation.id.header=X-Correlation-Id
kafka.correlation.id.header=cid
# --- Health ---
# List health-check routes that must all pass for /health to return 200.
# Add cloud.connector.health when cloud.connector != none.
# mandatory.health.dependencies=cloud.connector.health
# --- Actuators ---
protect.info.endpoints=false
# --- Serialization ---
snake.case.serialization=false
# --- Logging ---
log.format=text
# --- Cloud Connector (uncomment for service mesh) ---
# cloud.connector=kafka
# cloud.client.properties=file:/tmp/config/kafka.properties,classpath:/kafka.properties
See Also¶
- REST Automation — declarative REST endpoint configuration syntax
- Event Script Syntax — flow YAML configuration syntax
- Actuators & HTTP Client — built-in actuator endpoint reference