Arion reads a small set of environment variables at startup; each overrides the matching runtime field and its command-line flag, so the precedence is environment, then flag, then file.
Variables
| Variable | Value | Overrides | Description |
|---|---|---|---|
ARION_CPU_LIMIT | integer ≥ 1 | runtime.num_cpus | Cores to use. Checked before ARION_GATEWAY_CORES. |
ARION_GATEWAY_CORES | integer ≥ 1 | runtime.num_cpus | Cores to use, when ARION_CPU_LIMIT is unset. |
ARION_GATEWAY_RUNTIMES | integer ≥ 1 | runtime.num_runtimes | Number of Tokio worker runtimes. |
ARION_SERVICE_THREADS | integer ≥ 1 | runtime.num_service_threads | Threads for background service tasks. |
ARION_RT_GLOBAL_QUEUE_INTERVAL | integer ≥ 1 | runtime.global_queue_interval | Scheduler ticks between global queue polls. |
ARION_RT_EVENT_INTERVAL | integer | runtime.event_interval | Scheduler ticks between I/O event polls. |
ARION_RT_MAX_IO_EVENT_PER_TICK | integer ≥ 1 | runtime.max_io_events_per_tick | Maximum I/O events processed per tick. |
ARION_CODEMODE_POOL_CAPACITY | integer ≥ 1 | runtime.codemode.pool_capacity | Code-mode sandboxes the process can run at once. |
ARION_CODEMODE_MAX_MEMORY_BYTES | integer ≥ 1 | runtime.codemode.max_memory_bytes | Largest memory one code-mode sandbox may use, in bytes. |
RUST_LOG | filter string | logging.log_level | Process log filter, e.g. info or arion_lib=debug,info. |
ARION_CPU_LIMIT=4 ARION_GATEWAY_RUNTIMES=2 RUST_LOG=info arion -c arion.yamlA value that does not parse (for example ARION_CPU_LIMIT=abc or 0) is silently ignored and the next source in the precedence chain applies.
Variables named in the configuration
Wherever an Envoy DataSource appears in the configuration — TLS certificates and keys, trusted CA bundles, inline bodies — the environment_variable variant makes Arion read that value from a variable you name:
private_key:
environment_variable: ARION_TLS_KEYThe variable must be set when the config loads; a missing one fails with failed to read environment variable.
Build-time variables
CHANNEL_BODY_PREFETCH_FRAMES, EXT_PROC_BUFFERED_BODY_LIMIT, EXT_PROC_MERGE_WINDOW and EXT_PROC_FRAME_MERGE_LIMIT tune ext_proc internals but are read when the binary is compiled, not at runtime. Setting them on a running deployment has no effect.