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tomcat_exporter

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A Prometheus exporter for Apache Tomcat

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> NOTE: The official Prometheus [java client](https://github.com/prometheus/client_java) now supports some overlapping functionality like the [servlet filter](https://github.com/prometheus/client_java#servlet-filter). I suggest users to seriously consider to switch as you can expect more long term support from that implementation. I am considering sunsetting support for this exporter by the end of 2022.

# Prometheus Tomcat Exporter
A set of collectors that can be used to monitor Apache Tomcat instances.

### Available metrics
The following Tomcat related metrics are provided:

* Thread pool metrics
* Session metrics
* Request processor metrics
* Database connection pool metrics
* Tomcat version info
* Servlet response time metrics 
* Database response time metrics

### Using this library
If you are running Tomcat in the conventional non-embedded setup we recommended to add the following jars (see `pom.xml` for the correct versions) to the `$CATALINA_BASE/lib` directory or another directory on the Tomcat `common.loader` path.
Using the `common.loader` is important as we need to make sure that all metrics are registered using the same class loader.

* [simpleclient](https://search.maven.org/#search%7Cga%7C1%7Ca%3A%22simpleclient%22)
* [simpleclient_common](https://search.maven.org/#search%7Cga%7C1%7Ca%3A%22simpleclient_common%22)
* [simpleclient_servlet](https://search.maven.org/#search%7Cga%7C1%7Ca%3A%22simpleclient_servlet%22)
* [simpleclient_servlet_common](https://search.maven.org/#search%7Cga%7C1%7Ca%3A%22simpleclient_servlet_common%22)
* [simpleclient_hotspot](https://search.maven.org/#search%7Cga%7C1%7Ca%3A%22simpleclient_hotspot%22)
* [tomcat_exporter_client](https://search.maven.org/#search%7Cga%7C1%7Ca%3A%22tomcat_exporter_client%22)

Next, rename [tomcat_exporter_servlet](https://search.maven.org/#search%7Cga%7C1%7Ca%3A%22tomcat_exporter_servlet%22) war file to `metrics.war` and add it to the webapps directory of Tomcat. After restart of tomcat you should be able to access metrics via the `/metrics/` endpoint.

### Example Dockerfile 
The following Dockerfile provides an example how you include the exporter in a Tomcat image:

```
FROM tomcat:9.0-jdk17-openjdk-slim

ENV TOMCAT_SIMPLECLIENT_VERSION=0.12.0
ENV TOMCAT_EXPORTER_VERSION=0.0.15

RUN apt-get update && apt-get install -y curl && \
    curl -v --fail --location https://search.maven.org/remotecontent?filepath=io/prometheus/simpleclient/${TOMCAT_SIMPLECLIENT_VERSION}/simpleclient-${TOMCAT_SIMPLECLIENT_VERSION}.jar --output /usr/local/tomcat/lib/simpleclient-${TOMCAT_SIMPLECLIENT_VERSION}.jar && \
    curl -v --fail --location https://search.maven.org/remotecontent?filepath=io/prometheus/simpleclient_common/${TOMCAT_SIMPLECLIENT_VERSION}/simpleclient_common-${TOMCAT_SIMPLECLIENT_VERSION}.jar --output /usr/local/tomcat/lib/simpleclient_common-${TOMCAT_SIMPLECLIENT_VERSION}.jar && \
    curl -v --fail --location https://search.maven.org/remotecontent?filepath=io/prometheus/simpleclient_hotspot/${TOMCAT_SIMPLECLIENT_VERSION}/simpleclient_hotspot-${TOMCAT_SIMPLECLIENT_VERSION}.jar --output /usr/local/tomcat/lib/simpleclient_hotspot-${TOMCAT_SIMPLECLIENT_VERSION}.jar && \
    curl -v --fail --location https://search.maven.org/remotecontent?filepath=io/prometheus/simpleclient_servlet/${TOMCAT_SIMPLECLIENT_VERSION}/simpleclient_servlet-${TOMCAT_SIMPLECLIENT_VERSION}.jar --output /usr/local/tomcat/lib/simpleclient_servlet-${TOMCAT_SIMPLECLIENT_VERSION}.jar && \
    curl -v --fail --location https://search.maven.org/remotecontent?filepath=io/prometheus/simpleclient_servlet_common/${TOMCAT_SIMPLECLIENT_VERSION}/simpleclient_servlet_common-${TOMCAT_SIMPLECLIENT_VERSION}.jar --output /usr/local/tomcat/lib/simpleclient_servlet_common-${TOMCAT_SIMPLECLIENT_VERSION}.jar && \
    curl -v --fail --location https://search.maven.org/remotecontent?filepath=nl/nlighten/tomcat_exporter_client/${TOMCAT_EXPORTER_VERSION}/tomcat_exporter_client-${TOMCAT_EXPORTER_VERSION}.jar --output /usr/local/tomcat/lib/tomcat_exporter_client-${TOMCAT_EXPORTER_VERSION}.jar && \
    curl -v --fail --location https://search.maven.org/remotecontent?filepath=nl/nlighten/tomcat_exporter_servlet/${TOMCAT_EXPORTER_VERSION}/tomcat_exporter_servlet-${TOMCAT_EXPORTER_VERSION}.war --output /usr/local/tomcat/webapps/metrics.war
```

### Servlet response time metrics
If you want servlet response time metrics you can configure the `TomcatServletMetricsFilter` by adding it to the $CATALINA_BASE/conf/web.xml as shown below. There is no need to modify already deployed applications.

```xml
<filter>
  <filter-name>ServletMetricsFilter</filter-name>
  <filter-class>nl.nlighten.prometheus.tomcat.TomcatServletMetricsFilter</filter-class>
  <async-supported>true</async-supported>
  <init-param>
    <param-name>buckets</param-name>
    <param-value>.01, .05, .1, .25, .5, 1, 2.5, 5, 10, 30</param-value>
  </init-param>
</filter>

<filter-mapping>
  <filter-name>ServletMetricsFilter</filter-name>
  <url-pattern>/*</url-pattern>
</filter-mapping>
```
For an explanation on histograms and buckets please see the [prometheus documentation](https://prometheus.io/docs/concepts/metric_types/#histogram).

### Database response time metrics
Database response time metrics are only available when using the [Tomcat JDBC Pool](http://tomcat.apache.org/tomcat-8.5-doc/jdbc-pool.html) as this collector uses an interceptor mechanism that is only available for this type of pool.

The interceptor will collect the following metrics:

* A histogram with global query response times
* A histogram with per query response times for slow queries (optional)
* A gauge with per query error counts (optional)

Configuration is usually done in Tomcat's `server.xml` or `context.xml`

```xml
<Resource name="jdbc/TestDB"
           auth="Container"
           type="javax.sql.DataSource"
           factory="org.apache.tomcat.jdbc.pool.DataSourceFactory"
           jdbcInterceptors="nl.nlighten.prometheus.tomcat.TomcatJdbcInterceptor(logFailed=true,logSlow=true,threshold=1000,buckets=.01|.05|.1|1|10,slowQueryBuckets=1|10|30)"
           username="root"
           password="password"
           driverClassName="com.mysql.jdbc.Driver"
           url="jdbc:mysql://localhost:3306/mysql"/>
```

Configuration options of the interceptor are as shown above and have the following meaning:
- logFailed: if set to 'true' collect metrics on failed queries
- logSlow: if set to 'true' collect metrics on metrics exceeding threshold
- threshold: the threshold in ms above which metrics will be collected if logSlow=true
- buckets: the buckets separated by a pipe ("|") symbol to be used for the global query response times, defaults to .01|.05|.1|.25|.5|1|2.5|10
- slowQueryBuckets: the buckets separated by a pipe ("|") symbol to be used for the global query response times, defaults to 1|2.5|10|30

> NOTE: 
>- Enabling logFailed and logSlow may lead to a lot of additional metrics., so be careful !!!  
>- If you are defining your data source on application level (so inside your war), you need to set [bindOnInit](https://tomcat.apache.org/tomcat-9.0-doc/config/http.html#Standard_Implementation) to ensure that your data source has been initialized before the metrics application starts.

### Embedded mode
If you run Tomcat in embedded mode, please look at the `AbstractTomcatMetricsTest` for an example on how to configure the various exporters when running embedded.

### Javadocs
There are canonical examples defined in the class definition Javadoc of the client packages.

tomcat_exporter

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