Distributed tracing in HLD - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define the unique identifier used to track a request across services.

HLD

trace_id = generate_[1]()  # Unique ID for distributed tracing

Drag options to blanks, or click blank then click option'

Atraceparent

Bspan_id

Ctrace_context

Dtrace_id

Attempts:

3 left

💡 Hint

Common Mistakes

Confusing span_id with trace_id

Using trace_context instead of trace_id

The trace_id uniquely identifies a request as it travels through multiple services.

2fill in blank

medium

Complete the code to create a new span representing a unit of work in distributed tracing.

HLD

span = tracer.start_[1](name="database_query")

Drag options to blanks, or click blank then click option'

Atrace

Bspan

Ccontext

Dtrace_id

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'trace' instead of 'span' to start a unit of work

Confusing 'context' with span creation

A span represents a single operation or unit of work within a trace.

3fill in blank

hard

Fix the error in the code to correctly propagate trace context between services.

HLD

headers["[1]"] = serialize_trace_context(trace_context)

Drag options to blanks, or click blank then click option'

Atraceparent

Bspan_id

Ctrace_id

Dtracing_header

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'trace_id' as header name instead of 'traceparent'

Using non-standard header names

The traceparent header is the standard way to propagate trace context across service boundaries.

4fill in blank

hard

Fill both blanks to correctly extract and start a child span from incoming trace context.

HLD

incoming_context = extract_trace_context([1])
child_span = tracer.start_span(name="process_request", context=[2])

Drag options to blanks, or click blank then click option'

Arequest.headers

Bincoming_context

Ctrace_context

Drequest.body

Attempts:

3 left

💡 Hint

Common Mistakes

Extracting context from request body

Passing wrong variable as context to start_span

The trace context is extracted from the incoming request headers, then used to start a child span.

5fill in blank

hard

Fill all three blanks to build a dictionary representing a trace span with its ID, parent ID, and operation name.

HLD

span_info = {
  "span_id": [1],
  "parent_id": [2],
  "operation": "[3]"
}

Drag options to blanks, or click blank then click option'

Acurrent_span.id

Bparent_span.id

Cprocess_payment

Dtrace_id

Attempts:

3 left

💡 Hint

Common Mistakes

Using trace_id instead of span_id

Mixing up current_span and parent_span IDs

The span_id is the current span's ID, parent_id is the parent's ID, and operation is the name of the work done.

Practice

1. What is the main purpose of distributed tracing in a system?
TraceID and spans are used to:

easy

A. Balance load between servers automatically

B. Store user data securely in a database

C. Track requests as they move through multiple services

D. Encrypt communication between clients and servers

Solution

1. Step 1: Understand distributed tracing basics

   Distributed tracing helps track how a request flows through different parts of a system.

2. Step 2: Identify the role of TraceID and spans

   TraceID links all parts of a request, and spans represent each step or service involved.

3. Final Answer:

   Track requests as they move through multiple services -> Option C

4. Quick Check:

   Distributed tracing = Track requests [OK]

Hint: TraceID connects steps in request flow [OK]

Common Mistakes:

• Confusing tracing with data storage
• Mixing tracing with load balancing
• Thinking tracing encrypts data

2. Which of the following is the correct way to represent a span in distributed tracing data?

easy

A. "traceId:abc123;spanId:xyz789;operation:db_query"

B. { "traceId": "abc123", "spanId": "xyz789", "operation": "db_query" }

C. [ "traceId", "spanId", "operation" ]

D. abc123xyz789

Solution

1. Step 1: Identify correct data format for spans

   Spans are usually represented as structured data like JSON objects with keys and values.

2. Step 2: Compare options

   { "traceId": "abc123", "spanId": "xyz789", "operation": "db_query" } shows a JSON object with clear keys for traceId, spanId, and operation, which is standard.

3. Final Answer:

   { "traceId": "abc123", "spanId": "xyz789", "operation": "db_query" } -> Option B

4. Quick Check:

   Span = JSON object with keys [OK]

Hint: Spans use JSON key-value pairs [OK]

Common Mistakes:

• Using arrays instead of objects
• Using plain strings without structure
• Using XML tags incorrectly

3. Given the following trace data snippet:

{"traceId": "t1", "spans": [{"spanId": "s1", "parentId": null, "operation": "frontend"}, {"spanId": "s2", "parentId": "s1", "operation": "backend"}, {"spanId": "s3", "parentId": "s2", "operation": "db_query"}]}

What is the correct order of operations for this request?

medium

A. frontend -> backend -> db_query

B. db_query -> backend -> frontend

C. backend -> frontend -> db_query

D. frontend -> db_query -> backend

Solution

1. Step 1: Analyze parent-child relationships

   The span with parentId null is the root: frontend (s1). Backend (s2) is child of frontend, and db_query (s3) is child of backend.

2. Step 2: Determine operation order

   Request flows from frontend to backend to db_query following parent-child links.

3. Final Answer:

   frontend -> backend -> db_query -> Option A

4. Quick Check:

   Parent-child order = frontend to db_query [OK]

Hint: Follow parentId links from root span [OK]

Common Mistakes:

• Ignoring parentId null as root
• Reversing operation order
• Mixing span order in array with execution order

4. You notice that some spans in your distributed tracing system have missing traceId values. What is the most likely cause?

medium

A. The tracing library failed to propagate the traceId across services

B. The database storing traces is full

C. The network is too slow to send trace data

D. The user did not authenticate properly

Solution

1. Step 1: Understand traceId propagation

   TraceId must be passed along all services handling the request to link spans correctly.

2. Step 2: Identify cause of missing traceId

   If traceId is missing, it usually means the tracing library or instrumentation did not forward it properly.

3. Final Answer:

   The tracing library failed to propagate the traceId across services -> Option A

4. Quick Check:

   Missing traceId = propagation failure [OK]

Hint: Missing traceId means propagation error [OK]

Common Mistakes:

• Blaming storage or network issues
• Confusing authentication with tracing
• Assuming traceId is optional

5. You want to design a distributed tracing system for a microservices architecture with hundreds of services. Which approach best ensures scalability and minimal overhead?

hard

A. Store all trace data locally on each service without aggregation

B. Trace every request fully and store all spans in a single centralized database

C. Send trace data synchronously during each request to avoid data loss

D. Use sampling to trace only a subset of requests and store spans in a scalable backend

Solution

1. Step 1: Consider scalability challenges

   Tracing every request fully creates huge data and overhead, which is not scalable for hundreds of services.

2. Step 2: Evaluate best practices

   Sampling reduces data volume by tracing only some requests, and scalable backends handle storage efficiently.

3. Step 3: Assess other options

   Synchronous sending blocks requests, and local storage prevents global analysis.

4. Final Answer:

   Use sampling to trace only a subset of requests and store spans in a scalable backend -> Option D

5. Quick Check:

   Sampling + scalable storage = scalable tracing [OK]

Hint: Sample requests to reduce tracing load [OK]

Common Mistakes:

• Tracing all requests causing overload
• Synchronous sending blocking services
• Not aggregating trace data centrally