Set the server options every deployment needs · AI Engineering

A handful of server options decide who can reach the server, what name clients send, and what the log keeps.

Your first server works, and now other programs must call it. When you finish this section, you can set the address, the model name, the API key, the chat template, and the logging.

We did not measure the speed of these options. We checked the address, the model name, the API key, the YAML file, and the removed log flag on an L4 with the small Qwen3-0.6B. The rest comes from the vLLM documentation and the source at 0.31.0.

Pick the address and the port

Option	Default at 0.31.0	Set it when
`--host`	not set, so the server listens on every network interface	the server must answer only one interface, such as `127.0.0.1` for a local test
`--port`	8000	another program holds port 8000, or you run two servers on one machine

The default listens on every interface, so other machines on the network can reach the server. For a test on your own machine, set --host 127.0.0.1.

Give the model a stable name

By default, the model name in the API is the name you passed to vllm serve, such as Qwen/Qwen3-8B. Clients must send that exact name. --served-model-name sets the name that clients use instead:

bash

vllm serve Qwen/Qwen3-8B --served-model-name chat

Clients now send "model": "chat". You can then move to a new checkpoint without a change in the clients. The name also labels the metrics as model_name. If you give more than one name, the server answers to each of them.

Require an API key

--api-key makes the server require the key in the Authorization header. You can also set it with the VLLM_API_KEY environment variable, which keeps the key out of the process list.

Stop any server that already runs on port 8000. Then start the server with a key in the first terminal:

bash

VLLM_API_KEY=change-me vllm serve Qwen/Qwen3-8B --host 127.0.0.1 2>&1 | tee server.log

When the server is ready, send a request with the key from a second terminal:

bash

curl http://localhost:8000/v1/models -H "Authorization: Bearer change-me"

The key protects only the routes under /v1, /v2, /inference, and /cohere. Other routes on the same port, such as /invocations, /metrics, and /health, stay open. We checked this on an L4. Without the key, /v1/models returned 401. /health and /metrics returned 200, and so did a chat request to /invocations.

So the key does not make the server safe on a public network. Put a gateway in front of it, as the production page says.

Fix the chat template

vLLM formats chat messages with the chat template from the model repository. Some repositories have no template or a wrong one. Then the model sees a badly formatted prompt and answers poorly.

--chat-template takes a file path or the template text. --default-chat-template-kwargs sets template values for every request, such as '{"enable_thinking": false}' for Qwen3. A request can still set its own chat_template_kwargs. The reasoning models page uses this for Qwen3.

Control what the log keeps

Option	Default	What it does
`--enable-log-requests`	off	writes one line for each request, with its ID and parameters
`--max-log-len`	no limit	cuts the prompt text in those lines to this many characters
`VLLM_LOGGING_LEVEL`	`INFO`	sets the vLLM log level, such as `DEBUG` for a hard problem
`--uvicorn-log-level`	`info`	sets the log level of the HTTP server
`--disable-uvicorn-access-log`	off	removes the line for each HTTP request, such as each `/health` probe

With --enable-log-requests at the DEBUG level, the request lines include the prompt. Do not use that setting on a server that handles private data.

Older releases had a --disable-log-requests flag. At 0.31.0 that flag does not exist, and the request lines are off unless you turn them on.

Turn off usage statistics

vLLM sends anonymous usage data about the hardware and the model configuration by default. To turn it off, set VLLM_NO_USAGE_STATS=1 or DO_NOT_TRACK=1 in the environment of the server.

Keep the options in a file

vllm serve --config config.yaml reads the options from a YAML file. Each key is the long name of a flag without the two dashes, such as served-model-name: chat. An option on the command line wins over the same option in the file.

Check the options

Read the non-default args line near the top of the log. It lists every option that you changed from its default:

bash

grep "non-default args" server.log

Then call /v1/models with and without the key. Without it, the server returns HTTP 401.

Original source

- Set --host to 127.0.0.1 for a local test, because the default listens on every interface.
- Set --served-model-name, so clients keep one name across checkpoints.
- Use an API key and a gateway, because the key protects only some routes.

Sources: vLLM documentation at v0.31.0 (docs/configuration/serve_args.md, docs/usage/usage_stats.md, docs/usage/security.md, docs/usage/troubleshooting.md), the vLLM source at v0.31.0 (vllm/entrypoints/launchers/cli_args.py, vllm/entrypoints/launchers/launcher.py, vllm/engine/arg_utils.py, vllm/config/model.py, vllm/envs.py), capture/gpu/out-gb10/server-load-vllm.log, capture/gpu/out-l4/livecheck-2026-10-22.txt.