Streams

Containers, systemd and supervisord collect what a process writes to its standard error. StreamWriter writes there, or to any other stream PHP can open for appending: php://stdout, a named pipe, a device.

use Solo\Logger\Formatter\JsonFormatter;
use Solo\Logger\Logger;

$logger = Logger::stream(formatter: new JsonFormatter());

$logger->info('Worker started', ['queue' => 'mail']);
// stderr: {"time":"2026-11-01T09:30:00.123456+00:00","level":"info","message":"Worker started","context":{"queue":"mail"}}

Logger::stream() takes the stream — php://stderr by default — the minimum level, the formatter and the timezone, as Logger::file() takes a path. Built by hand:

use Solo\Logger\Writer\StreamWriter;

$logger = new Logger(new StreamWriter('php://stdout'), new JsonFormatter());

How It Writes

• The stream is opened on the first write and kept open; the constructor touches nothing.
• Each record goes out with its \n in one write. A pipe takes a write of up to PIPE_BUF bytes — 4 KiB on Linux — in one piece, so shorter records from processes that share a pipe never interleave.
• Nothing is locked or rotated, and no directory is created; a missing file is created in mode ab like any fopen(). For regular files, use FileWriter, which locks, rotates and creates directories.
• A stream that cannot be opened or written throws WriteException, as a file does.

Containers

Write JSON to standard error and let the runtime collect it:

$logger = Logger::stream(minLevel: LogLevel::INFO, formatter: new JsonFormatter());

Docker and Kubernetes split a line longer than 16 KiB into parts, which the collector has to join back. To keep records under that size, tighten the normalizer's limits:

use Solo\Logger\Context\ContextNormalizer;

$formatter = new JsonFormatter(normalizer: new ContextNormalizer(maxItems: 100, maxStringLength: 1024));

PHP-FPM

An FPM worker's standard error reaches the FPM log only with catch_workers_output = yes in the pool. Two more settings decide what the lines look like:

• decorate_workers_output = no keeps FPM from prefixing each line with the pool and the worker, which breaks JSON lines.
• log_limit, 1024 bytes by default, is the longest line FPM writes in one piece; it splits longer ones. Raise it above your largest record.

A File and Standard Error

use Psr\Log\LogLevel;
use Solo\Logger\Decorator\FanOutLogger;

$logger = new FanOutLogger(
    Logger::file('/var/log/app/app.log'),
    Logger::stream(minLevel: LogLevel::ERROR, formatter: new JsonFormatter()),
);

See Decorators.