Logging

How to view logs from the template build

You can retrieve the build logs using the SDK.

Default logger

We provide a default logger that you can use to filter logs by level:

JavaScript & TypeScript

import { Template, defaultBuildLogger } from 'e2b';

await Template.build(template, 'my-template', {
  onBuildLogs: defaultBuildLogger({
    minLevel: "info", // Minimum log level to show
  }),
});

from e2b import Template, default_build_logger

Template.build(
    template,
    'my-template',
    on_build_logs=default_build_logger(
        min_level="info",  # Minimum log level to show
    )
)

Custom logger

You can customize how logs are handled:

JavaScript & TypeScript

// Simple logging
onBuildLogs: (logEntry) => console.log(logEntry.toString());

// Custom formatting
onBuildLogs: (logEntry) => {
  const time = logEntry.timestamp.toISOString();
  console.log(`[${time}] ${logEntry.level.toUpperCase()}: ${logEntry.message}`);
};

// Filter by log level
onBuildLogs: (logEntry) => {
  if (logEntry.level === "error" || logEntry.level === "warn") {
    console.error(logEntry.toString());
  }
};

# Simple logging
on_build_logs=lambda log_entry: print(log_entry)

# Custom formatting
def custom_logger(log_entry):
    time = log_entry.timestamp.isoformat()
    print(f"[{time}] {log_entry.level.upper()}: {log_entry.message}")

Template.build(template, 'my-template', on_build_logs=custom_logger)

# Filter by log level
def error_logger(log_entry):
    if log_entry.level in ["error", "warn"]:
        print(f"ERROR/WARNING: {log_entry}", file=sys.stderr)

Template.build(template, 'my-template', on_build_logs=error_logger)

The onBuildLogs/on_build_logs callback receives structured LogEntry objects with the following properties:

JavaScript & TypeScript

type LogEntryLevel = 'debug' | 'info' | 'warn' | 'error'

class LogEntry {
  constructor(
    public readonly timestamp: Date,
    public readonly level: LogEntryLevel,
    public readonly message: string
  )

  toString() // Returns formatted log string
}

// Indicates the start of the build process
class LogEntryStart extends LogEntry {
  constructor(timestamp: Date, message: string) {
    super(timestamp, 'debug', message)
  }
}

// Indicates the end of the build process
class LogEntryEnd extends LogEntry {
  constructor(timestamp: Date, message: string) {
    super(timestamp, 'debug', message)
  }
}

LogEntryLevel = Literal["debug", "info", "warn", "error"]

@dataclass
class LogEntry:
    timestamp: datetime
    level: LogEntryLevel
    message: str

    def __str__(self) -> str:  # Returns formatted log string


# Indicates the start of the build process
@dataclass
class LogEntryStart(LogEntry):
    level: LogEntryLevel = field(default="debug", init=False)

# Indicates the end of the build process
@dataclass
class LogEntryEnd(LogEntry):
    level: LogEntryLevel = field(default="debug", init=False)

Together with the LogEntry type, there are also LogEntryStart and LogEntryEnd types that indicate the start and end of the build process. Their default log level is debug and you can use them to like this:

JavaScript & TypeScript

if (logEntry instanceof LogEntryStart) {
  // Build started
  return
}

if (logEntry instanceof LogEntryEnd) {
  // Build ended
  return
}

if isinstance(log_entry, LogEntryStart):
    # Build started
    return

if isinstance(log_entry, LogEntryEnd):
    # Build ended
    return