The Bundled Shield Sidecar

The elchi-client installer installs elchi-shield — the Envoy ext_proc API-security / WAF sidecar — by default, in the same run. On each edge host the client writes shield's policy files into a watched directory and shield inspects Envoy traffic over a local socket. This is the normal way to get shield onto an edge; you rarely install it separately.

Running Envoy without elchi-client?

If a host runs Envoy but not elchi-client, install shield on its own instead — see Standalone Shield Install.

Installed by default

Running the standard client installer already brings up shield alongside it:

sudo bash elchi-install.sh \
  --name=web-server-01 --host=backend.elchi.io --port=443 --tls=true --token=YOUR_TOKEN

The shield binary is fetched from the public elchi-archive mirror (bundled into the same release as the client installer), sha256-verified, and installed to /etc/elchi/bin/elchi-shield. A hardened elchi-shield.service systemd unit is written, enabled, and started. The shield version is pinned at release time by the elchi-archive workflow.

Skip or pin shield

Flag	Description
--no-shield	Do not install the shield sidecar (it is installed by default).
--shield-version=vX.Y.Z	Pin a specific elchi-shield release (default: the bundled/latest version).

# Install the client only, without the shield sidecar
sudo bash elchi-install.sh --no-shield --name=web-01 --host=… --port=443 --tls=true --token=…

These flags are also listed on the client installation page.

Audit and metrics sink config

Unlike the standalone installer (which stores the audit DSN in a systemd EnvironmentFile), the client writes one editable sink config file that shield reads via its --config-file:

/etc/elchi/elchi-shield/config.yaml   # mode 0600, owned by the elchi user

It holds the audit (ClickHouse) and metrics (OTLP) sink settings only — not the security policies. It may contain the ClickHouse DSN (with a password), so it is chmod 0600 and shield warns if it is group-readable. Set it at install time with:

Flag	Writes	Description
--shield-audit-dsn=DSN	audit.clickhouse_dsn (+ exporter: clickhouse)	Send shield audit events to central ClickHouse. Omit → exporter: none (audit off, no local file). Env: ELCHI_SHIELD_AUDIT_CLICKHOUSE_DSN.
--shield-metrics-otlp=H:P	metrics.otlp_endpoint	Push shield metrics to an OTel Collector (OTLP/gRPC). Omit → /metrics scrape only. Env: ELCHI_SHIELD_METRICS_OTLP_ENDPOINT.
--shield-metrics-insecure	metrics.otlp_insecure: true	Use plaintext gRPC to the metrics collector. Env: ELCHI_SHIELD_METRICS_OTLP_INSECURE.

The generated config.yaml looks like:

# elchi-shield SINK config — audit (ClickHouse) + metrics (OTLP).
# Edit, then:  systemctl restart elchi-shield
# Holds the ClickHouse DSN (may contain a password) — keep this file chmod 0600.
audit:
  # exporter: none | clickhouse | otel  (auto = clickhouse when a dsn is set)
  exporter: clickhouse
  # ClickHouse audit sink. e.g. clickhouse://user:pass@CH-HOST:9000/elchi
  clickhouse_dsn: "clickhouse://user:pass@ch.internal:9000/elchi"
  clickhouse_ttl_days: 7
metrics:
  # Push metrics to an OTel Collector (OTLP/gRPC host:port). Empty = /metrics scrape only.
  otlp_endpoint: "otel-collector:4317"
  otlp_insecure: false

You can also edit this file by hand after install and systemctl restart elchi-shield. If the file already exists on a re-run, the installer preserves it (re-asserting 0600) rather than overwriting your edits.

note

Legacy audit.env → config.yaml migration

Installs predating config.yaml stored the audit DSN in /etc/elchi/elchi-shield/audit.env. On upgrade, if you re-run without --shield-audit-dsn, the installer migrates the DSN out of audit.env into the new config.yaml (so audit isn't silently dropped), then removes the legacy file.

Where policies come from

The sink config above is separate from the security policies. Policies land as *.yaml files in the watched directory:

/etc/elchi/elchi-shield/conf.d/*.yaml

These are pushed from the Elchi control plane (via elchi-client) and hot-reloaded atomically — a bad file never affects live traffic. Authoring and structure are covered in Shield deployment.

Socket and endpoints

The client-installed unit mirrors the standalone layout:

Endpoint	Value
ext_proc UDS (Envoy connects here)	/run/elchi-shield/extproc.sock
Health / metrics (loopback)	127.0.0.1:9001
Watched policies	/etc/elchi/elchi-shield/conf.d
Data files	/etc/elchi/elchi-shield/files

The socket is a group-owned UDS under a systemd RuntimeDirectory; Envoy's user must be in the elchi group to reach it. The unit is hardened (NoNewPrivileges, ProtectSystem=strict, loopback-only HTTP) exactly like the standalone install. Wire Envoy to the socket per Envoy wiring; the full flag set is in the Shield reference.