Stage 3 · Build

Go Fundamentals for SREs

Error Handling Patterns

Sentinel errors, wrapping, fmt.Errorf, and error inspection for production reliability.

7 min readGo for SREBuild

Errors Are Values

In Go, errors are values — not exceptions. Every function that can fail returns an error value alongside its result. The caller checks the error explicitly. There is no try-catch, no stack unwinding, no hidden control flow.

Gothe-go-error-pattern.go

6 linesLn 1, Col 1Go

The pattern is consistent: check the error, wrap it with context, and return. The %w verb in fmt.Errorf wraps the original error while preserving the chain for inspection.

Sentinel Errors

Sentinel errors are package-level variables that define specific error conditions. Callers can compare against them using errors.Is to determine the exact failure reason.

Godefining-sentinel-errors.go

21 linesLn 1, Col 1Go

Sentinel errors give callers a clear, comparable error to handle. Use them for well-defined conditions that callers need to branch on. Don't create sentinels for every possible error.

Name sentinel errors with Err prefix

The convention is ErrSomething — ErrNotFound, ErrTimeout, ErrPermissionDenied. This makes them instantly recognizable as error values when reading code.

Error Wrapping with %w

Error wrapping adds context to errors as they propagate up the call stack. The %w verb in fmt.Errorf preserves the original error chain while adding a descriptive message.

Gowrapping-errors-with-context.go

18 linesLn 1, Col 1Go

Each error message adds context about where the error occurred. When you see an error in logs, the full chain tells you exactly what happened: reading config file /etc/cfg.yaml: parse error at line 5.

Error Inspection

errors.Is checks if any error in the chain matches a target. errors.As extracts a specific error type from the chain. These are the tools for handling wrapped errors correctly.

Goinspecting-error-chains.go

20 linesLn 1, Col 1Go

errors.Is walks the entire error chain, so it works even with deeply wrapped errors. errors.As does the same but extracts the first matching error into the target variable.

Custom Error Types

When sentinel errors are not enough, implement the error interface on a struct. Custom error types can carry structured data — HTTP status codes, error codes, retry hints — that callers can use programmatically.

Gocustom-error-type.go

22 linesLn 1, Col 1Go

Custom error types let callers inspect error details without parsing strings. The Retryable field makes it trivial for callers to decide whether to retry a failed operation.

Error Handling Patterns

Production error handling follows patterns. Handle errors at the right level, add context at each boundary, and never silently swallow errors.

Never ignore errors

The _ = err pattern hides bugs. If you genuinely cannot handle an error, log it and explain why. Silent failures are the hardest bugs to diagnose in production.

Goerror-propagation-pattern.go

22 linesLn 1, Col 1Go

Each error is handled at the appropriate level. Auth failures propagate up. Not-found returns a 404 response (not an error). Unknown store errors propagate with context. Transform errors propagate with context.

Mark this lesson complete to store local progress and unlock a cleaner resume path the next time you visit.

Stage 3 · Build

Go Fundamentals for SREs

Error Handling Patterns

Sentinel errors, wrapping, fmt.Errorf, and error inspection for production reliability.

7 min readGo for SREBuild

Errors Are Values

Gothe-go-error-pattern.go

6 linesLn 1, Col 1Go

The pattern is consistent: check the error, wrap it with context, and return. The %w verb in fmt.Errorf wraps the original error while preserving the chain for inspection.

Sentinel Errors

Sentinel errors are package-level variables that define specific error conditions. Callers can compare against them using errors.Is to determine the exact failure reason.

Godefining-sentinel-errors.go

21 linesLn 1, Col 1Go

Sentinel errors give callers a clear, comparable error to handle. Use them for well-defined conditions that callers need to branch on. Don't create sentinels for every possible error.

Name sentinel errors with Err prefix

The convention is ErrSomething — ErrNotFound, ErrTimeout, ErrPermissionDenied. This makes them instantly recognizable as error values when reading code.

Error Wrapping with %w

Error wrapping adds context to errors as they propagate up the call stack. The %w verb in fmt.Errorf preserves the original error chain while adding a descriptive message.

Gowrapping-errors-with-context.go

18 linesLn 1, Col 1Go

Error Inspection

errors.Is checks if any error in the chain matches a target. errors.As extracts a specific error type from the chain. These are the tools for handling wrapped errors correctly.

Goinspecting-error-chains.go

20 linesLn 1, Col 1Go

errors.Is walks the entire error chain, so it works even with deeply wrapped errors. errors.As does the same but extracts the first matching error into the target variable.

Custom Error Types

Gocustom-error-type.go

22 linesLn 1, Col 1Go

Custom error types let callers inspect error details without parsing strings. The Retryable field makes it trivial for callers to decide whether to retry a failed operation.

Error Handling Patterns

Production error handling follows patterns. Handle errors at the right level, add context at each boundary, and never silently swallow errors.

Never ignore errors

The _ = err pattern hides bugs. If you genuinely cannot handle an error, log it and explain why. Silent failures are the hardest bugs to diagnose in production.

Goerror-propagation-pattern.go

22 linesLn 1, Col 1Go

Mark this lesson complete to store local progress and unlock a cleaner resume path the next time you visit.