Most Used Docker Commands:Interview Question
Pre-Requisite:
What is Prometheus?
Prometheus is a free software application used for event monitoring and alerting. It records real-time metrics in a time series database (allowing for high dimensionality) built using a HTTP pull model, with flexible queries and real-time alerting.
Monitor Java Applications with Prometheus
This section will explain how an existing Java application can be updated to publish metrics and monitored by Prometheus.
Prometheus collects metrics from monitored targets by scraping metrics HTTP endpoints on these targets.
As discussed earlier, Prometheus collects metrics from monitored targets by scraping from an HTTP endpoint on these targets. By default, these metrics are expected to be published at /metrics. Any existing Java application can be updated to publish Prometheus-style metrics at this endpoint.
An earlier chapter explained a simple Java EE application that talks to a MySQL database. This application also publishes Prometheus-style metrics for the underlying JVM at /metrics. It also publishes application-specific metrics such as total number of times GET / and GET /{id} is called.
The complete set of JVM metrics are explained at https://github.com/prometheus/client_java. Refer to https://github.com/arun-gupta/docker-javaee/tree/master/employees/src/main/java/org/javaee/samples/employees/metrics for more details on how these metrics are enabled.
Start Java application
Use the Compose file to deploy a simple the Java EE application. This will start WildFly Swarm application and MySQL database.
docker stack deploy --compose-file=docker-compose.yml webapp
This will create
webapp_defaultoverlay network, and start thewebapp_webandwebapp_dbservices.Verify the network:
$ docker network ls NETWORK ID NAME DRIVER SCOPE u6ybdaqx5h5y webapp_default overlay swarmOther networks may be shown here as well.
Verify the services:
$ docker service ls ID NAME MODE REPLICAS IMAGE PORTS ucztcpf1vw0a webapp_db replicated 1/1 mysql:8 *:3306->3306/tcp jttfgvr09kre webapp_web replicated 1/1 arungupta/docker-javaee:latest *:8080->8080/tcp,*:9990->9990/tcpVerify that the endpoint is accessible:
$ curl http://localhost:8080/resources/employees <?xml version="1.0" encoding="UTF-8" standalone="yes"?><collection><employee><id>1</id><name>Penny</name></employee><employee><id>2</id><name>Sheldon</name></employee><employee><id>3</id><name>Amy</name></employee><employee><id>4</id><name>Leonard</name></employee><employee><id>5</id><name>Bernadette</name></employee><employee><id>6</id><name>Raj</name></employee><employee><id>7</id><name>Howard</name></employee><employee><id>8</id><name>Priya</name></employee></collection>Access the metrics published by the endpoint using
curl http://localhost:8080/metricsto see the output:# HELP jvm_info JVM version info # TYPE jvm_info gauge jvm_info{version="1.8.0_141-8u141-b15-1~deb9u1-b15",vendor="Oracle Corporation",} 1.0 # HELP jvm_gc_collection_seconds Time spent in a given JVM garbage collector in seconds. # TYPE jvm_gc_collection_seconds summary jvm_gc_collection_seconds_count{gc="PS Scavenge",} 25.0 jvm_gc_collection_seconds_sum{gc="PS Scavenge",} 0.386 jvm_gc_collection_seconds_count{gc="PS MarkSweep",} 6.0 jvm_gc_collection_seconds_sum{gc="PS MarkSweep",} 0.546 # HELP process_cpu_seconds_total Total user and system CPU time spent in seconds. # TYPE process_cpu_seconds_total counter process_cpu_seconds_total 25.5 # HELP process_start_time_seconds Start time of the process since unix epoch in seconds. # TYPE process_start_time_seconds gauge process_start_time_seconds 1.508056592419E9 # HELP process_open_fds Number of open file descriptors. # TYPE process_open_fds gauge process_open_fds 499.0 # HELP process_max_fds Maximum number of open file descriptors. # TYPE process_max_fds gauge process_max_fds 1048576.0 # HELP process_virtual_memory_bytes Virtual memory size in bytes. # TYPE process_virtual_memory_bytes gauge process_virtual_memory_bytes 4.244393984E9 # HELP process_resident_memory_bytes Resident memory size in bytes. # TYPE process_resident_memory_bytes gauge process_resident_memory_bytes 5.06601472E8 # HELP jvm_classes_loaded The number of classes that are currently loaded in the JVM # TYPE jvm_classes_loaded gauge jvm_classes_loaded 13096.0 # HELP jvm_classes_loaded_total The total number of classes that have been loaded since the JVM has started execution # TYPE jvm_classes_loaded_total counter jvm_classes_loaded_total 13096.0 # HELP jvm_classes_unloaded_total The total number of classes that have been unloaded since the JVM has started execution # TYPE jvm_classes_unloaded_total counter jvm_classes_unloaded_total 0.0 # HELP jvm_threads_current Current thread count of a JVM # TYPE jvm_threads_current gauge jvm_threads_current 60.0 # HELP jvm_threads_daemon Daemon thread count of a JVM # TYPE jvm_threads_daemon gauge jvm_threads_daemon 12.0 # HELP jvm_threads_peak Peak thread count of a JVM # TYPE jvm_threads_peak gauge jvm_threads_peak 67.0 # HELP jvm_threads_started_total Started thread count of a JVM # TYPE jvm_threads_started_total counter jvm_threads_started_total 93.0 # HELP jvm_threads_deadlocked Cycles of JVM-threads that are in deadlock waiting to acquire object monitors or ownable synchronizers # TYPE jvm_threads_deadlocked gauge jvm_threads_deadlocked 0.0 # HELP jvm_threads_deadlocked_monitor Cycles of JVM-threads that are in deadlock waiting to acquire object monitors # TYPE jvm_threads_deadlocked_monitor gauge jvm_threads_deadlocked_monitor 0.0 # HELP jvm_memory_bytes_used Used bytes of a given JVM memory area. # TYPE jvm_memory_bytes_used gauge jvm_memory_bytes_used{area="heap",} 1.2072508E8 jvm_memory_bytes_used{area="nonheap",} 9.3550048E7 # HELP jvm_memory_bytes_committed Committed (bytes) of a given JVM memory area. # TYPE jvm_memory_bytes_committed gauge jvm_memory_bytes_committed{area="heap",} 2.69484032E8 jvm_memory_bytes_committed{area="nonheap",} 1.0133504E8 # HELP jvm_memory_bytes_max Max (bytes) of a given JVM memory area. # TYPE jvm_memory_bytes_max gauge jvm_memory_bytes_max{area="heap",} 4.66092032E8 jvm_memory_bytes_max{area="nonheap",} -1.0 # HELP jvm_memory_pool_bytes_used Used bytes of a given JVM memory pool. # TYPE jvm_memory_pool_bytes_used gauge jvm_memory_pool_bytes_used{pool="Code Cache",} 1.4589888E7 jvm_memory_pool_bytes_used{pool="Metaspace",} 6.9998048E7 jvm_memory_pool_bytes_used{pool="Compressed Class Space",} 8962112.0 jvm_memory_pool_bytes_used{pool="PS Eden Space",} 2.3732032E7 jvm_memory_pool_bytes_used{pool="PS Survivor Space",} 6073592.0 jvm_memory_pool_bytes_used{pool="PS Old Gen",} 9.0919456E7 # HELP jvm_memory_pool_bytes_committed Committed bytes of a given JVM memory pool. # TYPE jvm_memory_pool_bytes_committed gauge jvm_memory_pool_bytes_committed{pool="Code Cache",} 1.47456E7 jvm_memory_pool_bytes_committed{pool="Metaspace",} 7.5800576E7 jvm_memory_pool_bytes_committed{pool="Compressed Class Space",} 1.0788864E7 jvm_memory_pool_bytes_committed{pool="PS Eden Space",} 9.2274688E7 jvm_memory_pool_bytes_committed{pool="PS Survivor Space",} 3.8797312E7 jvm_memory_pool_bytes_committed{pool="PS Old Gen",} 1.38412032E8 # HELP jvm_memory_pool_bytes_max Max bytes of a given JVM memory pool. # TYPE jvm_memory_pool_bytes_max gauge jvm_memory_pool_bytes_max{pool="Code Cache",} 2.5165824E8 jvm_memory_pool_bytes_max{pool="Metaspace",} -1.0 jvm_memory_pool_bytes_max{pool="Compressed Class Space",} 1.073741824E9 jvm_memory_pool_bytes_max{pool="PS Eden Space",} 9.699328E7 jvm_memory_pool_bytes_max{pool="PS Survivor Space",} 3.8797312E7 jvm_memory_pool_bytes_max{pool="PS Old Gen",} 3.49700096E8It shows all the JVM metrics that are published by the Prometheus JVM Client. The metrics generated by the application are not shown yet. It requires for the application to be accessed first.
Let’s access the JVM metrics in Prometheus dashboard first, and then we’ll access the app to show app-specific metrics.
Start Prometheus service
Make sure to terminate any previously running Prometheus endpoints:
docker service rm metrics
Create a directory
prometheusand change into that directory.Create a text file
prometheus.ymland add the following content:global: scrape_interval: 10s scrape_configs: - job_name: 'webapp' dns_sd_configs: - names: ['tasks.webapp_web'] type: 'A' port: 8080This defines the configuration for the HTTP endpoint that publishes Prometheus-style metrics from the Java application.
Start Prometheus service:
docker service create \ --replicas 1 \ --network webapp_default \ --name metrics \ --mount type=bind,source=`pwd`/prometheus.yml,destination=/etc/prometheus/prometheus.yml \ --publish 9090:9090 \ prom/prometheusNote, this service is using the
webapp_defaultoverlay network that is created when the application stack was deployed.Access Prometheus dashboard at http://localhost:9090
Check the configured targets at http://localhost:9090/targets:
It shows that the application metrics HTTP endpoint is configured as a Prometheus target.
View application metrics
On Prometheus dashboard, click on
-insert metric at cursor-to see the list of metrics available:
JVM metrics shown earlier are displayed here as well.
Select
jvm_memory_pool_bytes_usedmetric and click onExecuteto view the metric.
Select
Graphto view the graphical representation
Now access the application using
curl http://localhost:8080/resources/employeesa few times.Refresh Prometheus dashboard and see the updated list of metrics:
Note,
app*andrequests*that are generated by the application.Select
requests_get_allmetric and view the graph:
Access the application a few times using
curl http://localhost:8080/resources/employees/5and then watch therequests_get_onemetric.
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