Datadog Agent: no metrics after migrating from Nagios/Zabbix/CloudWatch

# General agent status - Forwarder, API Keys, Collector sections
sudo datadog-agent status | sed -n '1,60p'

# Typical problem signals:
#   "API Key is invalid" / "403 Forbidden"        -> wrong API key or wrong site (region)
#   "Forwarder ... Errors: N" / "Transactions dropped"  -> intake connectivity
#   integration missing from the "Checks" section or "Instances: 0"  -> integration not enabled
#   host visible, but metrics without the expected tags  -> inconsistent tags

# Whether the agent delivers data to intake at all
sudo datadog-agent status | grep -A5 "Forwarder"

# Test connectivity to the intake endpoint (site-dependent!)
curl -v "https://api.datadoghq.eu/api/v1/validate" \
  -H "DD-API-KEY: ${DD_API_KEY}" 2>&1 | tail -5
# Note: datadoghq.eu (EU) vs datadoghq.com (US) - wrong site = 403 despite a valid key

# Check which site the agent targets and whether the key is valid
sudo grep -E '^site:|^api_key:' /etc/datadog-agent/datadog.yaml
# For an EU account it must be:  site: datadoghq.eu

# Validate the key against the correct site
curl -s "https://api.datadoghq.eu/api/v1/validate" \
  -H "DD-API-KEY: ${DD_API_KEY}" | grep -q '"valid":true' && echo OK || echo FAIL
# FAIL -> wrong key or wrong site. Fix datadog.yaml and restart the agent:
sudo systemctl restart datadog-agent

# Forwarder section in the status: are there dropped transactions
sudo datadog-agent status | grep -A8 "Forwarder"

# Required outbound 443 connectivity to (for EU) among others:
#   *-app.agent.datadoghq.eu, api.datadoghq.eu, orch.datadoghq.eu
nc -vz api.datadoghq.eu 443

# If traffic goes through a proxy - configure the proxy in datadog.yaml:
# proxy:
#   https: "http://proxy.company.local:3128"
sudo systemctl restart datadog-agent

# Example: PostgreSQL integration - create the config from the template
sudo cp /etc/datadog-agent/conf.d/postgres.d/conf.yaml.example \
        /etc/datadog-agent/conf.d/postgres.d/conf.yaml
# Fill in host/port/monitoring user, then restart the agent
sudo systemctl restart datadog-agent

# Check that the integration collects metrics (Instances > 0, Metrics > 0)
sudo datadog-agent check postgres | grep -E "Instances|Metrics|Errors"
# Expected: Instances: 1, Metrics: >0, Errors: 0

# Set global tags in datadog.yaml, consistent with the migrated dashboards/monitors
# tags:
#   - env:prod
#   - team:platform
# For application metrics, set service/env in the integration config or via autodiscovery.

# Verify the host tags after restart
sudo datadog-agent status | grep -A10 "Host Info"
# Make sure the tag keys (env, service) match by name and value
# the filters in the migrated dashboards - otherwise the views stay empty.

# 1. Agent status without key or forwarder errors
sudo datadog-agent status | grep -E "API Keys|Forwarder" -A3
# Expected: key "valid", no dropped transactions

# 2. The host reports and is visible (validate the key against the correct site)
curl -s "https://api.datadoghq.eu/api/v1/validate" -H "DD-API-KEY: ${DD_API_KEY}"
# Expected: {"valid":true}

# 3. Each required integration collects metrics
for c in postgres nginx disk; do
  echo "== $c =="; sudo datadog-agent check $c | grep -E "Instances|Metrics|Errors"
done
# Expected: Instances > 0, Metrics > 0, Errors: 0 for each integration

# 4. Tags consistent with the dashboards (env/service present)
sudo datadog-agent status | grep -A10 "Host Info" | grep -E "env:|service:"
# Expected: tags present and matching the filters in the migrated dashboards