Logging is available in Spring by default provided by SLF4J (Simple Logging Facade 4 Java) implemented by Apache Logback, successor to the infamous Log4j. We don’t need any dependencies for these separately.
// in Foobar.java
Logger log = LoggerFactory.getLogger(Foobar.class);
log.trace("A TRACE Message");
log.debug("A DEBUG Message");
log.info("An INFO Message"); // base level by default; this and all above this are shown
log.warn("A WARN Message");
log.error("An ERROR Message");
log.error("A Message with a value {}", valueVar); // cleaner syntax with log
// we can use lombok too to avoid line 1 above
@Slf4j // creates slf4j logger
// or
@CommonsLog // creates Apache commons log
// logger variable is named "log"
Control logs using properties
# log level for the entire app
logging.level.root=TRACE
# package specific
logging.level.com.test.repository=INFO
# package specific for framework level logs
logging.level.org.springframework.web=debug
logging.level.org.hibernate=error
# group packages
logging.group.foobar=com.test.repository,com.test.service
logging.level.foobar=DEBUG
# log file (created in root dir by default)
logging.file.name=myapp.log
MDC provides a way to enrich log messages with information that could be unavailable in the scope where the logging actually occurs but that can be indeed useful to better track the execution of the program.
What if we want to log userId of every request coming in? We can do so by setting MDC.put("userId", userId) and accessing via log pattern so that userId is printed in every line in the console. It is thread-local too, which means it will only remember it for that particular request only.
Reference: https://www.youtube.com/watch?v=tmj6QphzAPo&t=1019s
We can use it to specify logging properties separate from application.properties file.
Old way is to use logback.xml and Spring will use that if it is present, otherwise the newer Logback Spring Extension (logback-spring.xml) is preferred.
Metrics collection and storage (Prometheus) and metrics and log visualization (Grafana).
Micrometer is the default facade provided by Spring for metrics, just like Slf4j for logs.
micrometer-registry-prometheus dependency adds an endpoint /actuator/prometheus which lists all metrics for the appSPRING BOOT APP <--polls-- PROMETHEUS <--polls-- GRAFANA
Config polling interval and other settings in a Prometheus.yml file on the Prometheus server. It has its own local time-series database to store metrics history.
We see logs in Grafana but without the distributed tracing.
We can also configure metrics export to other dashboards and Time-Series DB like Datadog and Influx DB. As well as configure alerts to Slack etc using Web Hooks in case an anomaly is detected.
We used Zipkin and Sleuth (deprecated) here inorder to trace logs for a request going through multiple services.
Zipkin server JAR is downloaded and runs separately. We need to include Zipkin client and Micrometer dependencies in services.
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-sleuth-zipkin</artifactId>
</dependency>
<!-- below is deprecated; in Spring Boot 3.0, use Micrometer dependency -->
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-starter-sleuth</artifactId>
</dependency>
spring:
application:
name: USER-SERVICE
zipkin:
base-url: http://localhost:9411 # Zipkin server URL
TraceId - One ID for a request no matter how many services it calls
SpanId - This keeps changing for every service we call in the path while fulfilling a request
2022-06-20 11:18:54.720 INFO [DEPARTMENT-SERVICE,5ec01b4d1b55f35f,f3aeb60a7471c5af] 21340 --- [nio-9002-exec-1] o.a.c.c.C.[Tomcat].[localhost].[/]
# INFO [service-name, traceId, spanId]
We can also create out own Span IDs manually using methods from spring-cloud-sleuth (or micrometer) (in code).
Step 1 - Logstash pulls logs from the app
Step 2 - Elasticsearch filter logs (index)
Step 3 - Kibana UI dashboard
All three run on their own dedicated server separate from our Spring Boot app.
Reference: ELK with Spring Boot Microservices - YouTube
Loki - Log Aggregation
Tempo - Distributed Tracing
Grafana - UI Dashboard
Use Prometheus for collecting metrics.
Reference: https://programmingtechie.com/2023/09/09/spring-boot3-observability-grafana-stack/
Splunk