Status
Current state: Draft
Proof of concept demo available here: https://github.com/yukim/cassandra-opentelemetry-demo
Discussion thread: -
JIRA: -
Released: -
Please keep the discussion on the mailing list rather than commenting on the wiki (wiki discussions get unwieldy fast).
Scope
- Provide unified way of exporting tracing, metrics, and logging to external monitoring system with ease of configuration
- Exporting repair tracing is out-of-scope in this proposal.
Goals
The goal of this proposal is to integrate OpenTelemetry into Apache Cassandra so that exporting telemetries and setting up the monitoring system is much easier.
This feature is opt-in and does not remove the currently available telemetries and the way to export.
Approach
While the goal of this CEP is to integrate OpenTelemetry features to be able to export tracing, metrics and logs, the proposal is separated into several steps.
OpenTelemetry spec and libraries are still evolving. Opentelemetry Java library provides stable support for Tracing and Metrics, however Logging support is experimental, as of the time of writing (May 2023).
See https://opentelemetry.io/status/ for up to date status.
The implementation will be separated in three parts:
- Configuration and OpenTelemetry Tracing integration
- OpenTelemetry Metrics integration
- OpenTelemetry Logging integration
Timeline
todo
Mailing list / Slack channels
Mailing list:
Slack channel:
Discussion threads:
Related JIRA tickets
JIRA(s):
- -
Motivation
Troubleshooting Apache Cassandra can be time-consuming and challenging when faced with failures or performance issues. Without a proper observability system in place, it becomes difficult to identify the root cause of these problems.
Apache Cassandra already implements its own methods or relies on external libraries to provide operators and administrators with deep insights into the complex distributed database using the three pillars of observability: Tracing, Metrics, and Logging.
- For tracing, Apache Cassandra has its own Tracing API.
- For metrics collection and reporting, Apache Cassandra uses Codahale’s Metrics library to collect and expose through JMX.
- For the logging, Apache Cassandra uses Slf4J/Logback logging library.
However, these features become significantly more valuable when available within an observability system that can correlate these telemetries together. Otherwise, operators and admins are left manually pulling out individual telemetries and assembling information by hand to make assumptions about the root cause of a problem.
To implement observability in Apache Cassandra, operators must devise their own methods to extract these telemetries and establish a monitoring stack. This often involves using open-source software like Prometheus/Grafana or commercial services like Datadog. The process of setting up the stack varies depending on the software used, making it complex and oftentimes overlooked by operators.
OpenTelemetry is the project hosted at CNCF to provide "A single, vendor-agnostic instrumentation library per language with support for both automatic and manual instrumentation"(https://opentelemetry.io/docs/concepts/what-is-opentelemetry/). It specifies APIs to collect tracing, metrics, and logging, and protocols to export to the external observation software.
Introducing OpenTelemetry makes exporting telemetries and integrating observability software much easier, requiring fewer configurations. It also enables observability software projects, vendors, and service providers to develop Cassandra-specific solutions based on the standardized semantics provided by this CEP and OpenTelemetry spec.
Audience
- Cassandra contributors / DevOps / DBAs
- APM, Observation OSS projects / software venders / service providers
Proposed Changes
This CEP aims to integrate OpenTelemetry Tracing, Metrics and Logging with the existing implementations (Cassandra’s own Tracing API, Codahale/Dropwizard metrics, and Slf4J/Logback), while maintaining the backward compatibility.
Configuration
Apache Cassandra uses OpenTelemetry SDK to manually instrument itself to export tracing, metrics and logs. Operators can configure how these telemetry are exported to the external system by changing the configuration in cassandra.yaml
file and either jvm-server.options
file or environmental variables.
Apache Cassandra uses OpenTelemetry SDK Autoconfigure to configure OpenTelemetry exporters.
By default, only the OTLP exporter jars are included in the Apache Cassandra distribution, and when enabled, Apache Cassandra starts exporting telemetries to OTLP collector running in localhost:4317 through grpc.
Operators can provide the necessary jars and configuration to use other exporters (i.e. <appender name="OpenTelemetry"
class="io.opentelemetry.instrumentation.logback.appender.v1_0.OpenTelemetryAppender">
</appender> for tracing) as well. For example, if you want to export tracing to Jaeger, you need to add opentelemetry-exporter-jaeger.jar
file in the classpath, and configure through jvm-server.options
:
# jvm-server.options
# Configure tracing export to Jaeger
-Dotel.traces.exporter=jaeger
-Dotel.exporter.jaeger.endpoint=http://jaeger:14250
OpenTelemetry can be configured using environmental variables as well. This is useful for containerized environment like Kubernetes.
Exporting Trace through OpenTelemetry
OpenTelemetry Tracing root Span
will be created when a coordinator node receives the message from the client (the same timing when Cassandra Tracing starts).
In order to avoid re-instrumenting code with OpenTelemetry API, Tracing
object will produce OpenTelemetry tracing event when its trace
method is called. Note that OpenTelemetry Tracing will not produce anything when it is not enabled.
Context propagation
From the client to Cassandra node through Native Protocol
The CEP proposes standardized way to propagate OpenTelemetry Context
from the applications through Native Protocol’s custom payload, rather than introducing new header definitions.
By using custom payload, the clients can easily start propagating Context
without upgrading the driver they are using.
Right now, only text propagator based on W3C Trace Context is officially defined and provided. Binary propagator will be added in the future (https://github.com/open-telemetry/opentelemetry-specification/issues/437).
By following the W3C standard, the CEP proposes to use the following custom payload key value pairs to propagate OpenTelemetry Context
:
Name | Description | Type of value | Example value |
---|---|---|---|
traceparent | The same header as W3C Trace Context carrying parent tracing information. https://www.w3.org/TR/trace-context/#traceparent-header | String | 00-0af7651916cd43dd8448eb211c80319c-b7ad6b7169203331-01 |
tracestate | The same header as W3C Trace Context carrying vendor specific information. https://www.w3.org/TR/trace-context/#tracestate-header | String | vendorname1=opaqueValue1,vendorname2=opaqueValue2 |
In the client side, we can use the standard class to inject the Context
into custom payload. For java, it would be like:
Map<String, ByteBuffer> payload = new HashMap<>();
W3CTraceContextPropagator.getInstance().inject(Context.current(), payload, (carrier, key, value) -> {
if (carrier != null) {
carrier.put(key, ByteBuffer.wrap(value.getBytes(StandardCharsets.UTF_8)));
}
});
Statement<?> injected = statement.setCustomPayload(payload);
session.execute(injected);
Between nodes through inter-node messaging protocol
To propagate OpenTelemetry Context
between the nodes, the sender adds the new ParamType
to the message only when:
- The message is a request message (not response message).
- Current
Span
is recording.- This is to prevent creating unnecessary root Spans for every Message Verbs.
The new ParamType Context takes the following values from the current Context.
- Trace parent info
- trace id
- Span Id
- Flags
- Trace state
Upon receiving the message containing Context ParamType, the receiver constructs the remote span context, which becomes the parent of the span in this node.
Between threads through ExecutorLocals
Like Cassandra TracingState
, OpenTelemetry Context
will be held in ExecutorLocals
to propagate Context
between threads. Alternatively, Context
can be directly passed to Runnable
s to propagate context between threads.
List of Attribute
s associated in Tracing
The following Attribute
s are associated to Span
s and events. Attribute
names should follow the Attribute Naming rule.
Name | Description | Example value |
---|---|---|
cassandra.query.message_type | Message type of the query (QUERY / EXECUTE / BATCH / PREPARE) | QUERY |
cassandra.query.client.ip | Client IP address | |
cassandra.query.coordinator.ip cassandra.query.coordinator.port | Coordinator node’s broadcast rpc address and native transport port | 10.0.0.1 9042 |
cassandra.query.page_size | 5000 | |
cassandra.query.consistency_level | ||
cassandra.query.serial_consistency_level | ||
cassandra.net.verb | ||
net.peer.ip net.peer.port | ||
thread.name | Name of the thread when the event is recorded | MutationStage-1 |
thread.id | ID of the thread when the event is recorded | 105 |
Exporting Metrics through OpenTelemetry
Cassandra is already instrumented by Dropwizard Metrics library. Instead of rewriting every metrics with OpenTelemetry SDK, create OpenTelemetry adapter using MetricRegistryListener.
OpenTelemetry MetricRegistryListener
is registered only when OpenTelemetry feature is enabled in cassandra.yaml.
This adapter uses OpenTelemetry Metrics SDK's asynchronous instrument variants to record metrics from the original Dropwizard metrics counterpart upon collection.
https://opentelemetry.io/docs/instrumentation/java/manual/#metrics
Exporting Logging through OpenTelemetry
Using Logback Adapter library, Apache Cassandra can directly export log to the collector without changing the current logging code in Apache Cassandra.
https://opentelemetry.io/docs/instrumentation/java/manual/#logs
Operators need to activate OpenTelemetry appender in logback.xml
New or Changed Public Interfaces
New org.apache.cassandra.telemetry.Telemetry
class
- Holds the global
io.opentelemtry.api.OpenTelemetry
instance. - Initialize
OpenTelemetry
instance using OpenTelemetry SDK Autoconfigure whenopentelemetry
configuration incassandra.yaml
hasenabled: true
.- By using
OpenTelemetry SDK Autoconfigure
, users can configure OpenTelemetry exporters through Java system properties and environmental variables.
- By using
- By default, OpenTelemetry is disabled.
- When OpenTelemetry is disabled, No-Op
OpenTelemetry
related instances are created through OpenTelemetry SDK.
- When OpenTelemetry is disabled, No-Op
- Sets up OpenTelemetry tracing, metrics and logs providers.
New cassandra.yaml entry
# Export Apache Cassandra telemetries(tracing, metrics and logs)
# through OpenTelemetry.
#
# Use jvm-server.options file to configure OpenTelemetry SDK with
# system properties.
# <https://github.com/open-telemetry/opentelemetry-java/tree/main/sdk-extensions/autoconfigure>
# Apache Cassandra only comes with the libraries to export telemetry
# through OLTP.
# You need appropriate jar files if you plan to use other exporters.
opentelemetry:
enabled: false # default: false
Necessary config change
-Xss
needs to be increased (from 256k to 512k) for OLTP export (Okhttp3 based gRPC call) to work
New library dependencies
The following dependencies will be added to the distribution.
OpenTelemetry instrumentation and configuration
- io.opentelemetry:opentelemetry-api
- io.opentelemetry:opentelemetry-sdk
- io.opentelemetry:opentelemetry-sdk-extension-autoconfigure
Runtime dependencies for exporting via OTLP
- io.opentelemetry:opentelemetry-exporter-otlp
Extra dependencies to consider
- io.opentelemetry.instrumentation:opentelemetry-runtime-metrics
- The library to enable JVM metrics instrumentation
- io.opentelemetry:opentelemetry-exporter-otlp-logs
- Necessary if Apache Cassandra decides to adapt unstable OpenTelemetry Log export. The library is separated at the moment, with
-alpha
in its version.
- Necessary if Apache Cassandra decides to adapt unstable OpenTelemetry Log export. The library is separated at the moment, with
- io.opentelemetry.instrumentation::opentelemetry-logback-appender-1.0
- The library to enable exporting logs through Logback appender
Semantic convention
OpenTelemetry Resource
s are immutable attributes (key-value pairs) that describes the entity producing telemetries, in this case, Apache Cassandra server itself. Resource
s are created once when configuring OpenTelemetry, and those are associated to every telemetries produced by Apache Cassandra.
See Attribute Naming for the specification of naming of Resource
s.
Namespacing
Every Attribute
names (including Resource
names) begin with cassandra
. For example, to describe Cassandra version, the Resource name will be cassandra.version
.
Note that this namespace is used by OpenTelemetry’s JMX metrics gatherer already, however, since the source entity of telemetries is Apache Cassandra, conflicting with JMX metric gatherer shouldn’t be a problem.
List of Resources provided by Apache Cassandra
The following Resource
s are proposed to be configured when OpenTelemetry is enabled. OpenTelemetry standard Resource
s as well as Cassandra specific Resource
s are configured.
Resource name | Value | Description | Example |
---|---|---|---|
service.name | cassandra | • This is required Resource to be set by OpenTelemetry. | |
• It is possible to override this value through https://github.com/open-telemetry/opentelemetry-java/tree/main/sdk-extensions/autoconfigure#opentelemetry-resource or https://opentelemetry.io/docs/reference/specification/sdk-environment-variables/#general-sdk-configuration. | |||
service.namespace | Apache Cassandra cluster name | Test Cluster | |
service.instance.id | Apache Cassandra Host ID | 058321f5-29b3-4f12-9766-2ad793adb3a0 | |
service.version | Apache Cassandra version in use | 5.0.0 | |
net.host.ip / net.host.port | Apache Cassandra node’s endpoint address (listen_address or broadcast_address) and port | 192.168.1.1 and 7000 |
TODO
- Should we use Cassandra specific Resources such as
cassandra.cluster.name
over standard convention likeservice.namespace
?- Using standard may be better to use existing telemetry services.
- Do we need anything else?
Compatibility, Deprecation, and Migration Plan
OpenTelemetry integration adds capability to export existing Tracing/Metrics/Logs through OpenTelemetry Protocol. This feature will not prevent existing telemetry collection. Users should be able to use existing Cassandra tracing, export Metrics through JMX, and output logs to files.
Test Plan
OpenTelemetry Java library provides in-memory telemetry sinks for testing. Use it to verify the exported telemetries.
Rejected Alternatives
- Apache Skywalking project provides similar protocol to export observability, however, there seems no APMs that support the Apache Skywalking protocol other than Apache Skywalking itself.