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Version: 3.3

Health Check

Description#

This article mainly introduces the health check function of Apache APISIX. The health check function can proxy requests to healthy nodes when the upstream node fails or migrates, avoiding the problem of service unavailability to the greatest extent. The health check function of APISIX is implemented using lua-resty-healthcheck, which is divided into active check and passive check.

Active check#

Active health check mainly means that APISIX actively detects the survivability of upstream nodes through preset probe types. APISIX supports three probe types: HTTP, HTTPS, and TCP.

When N consecutive probes sent to healthy node A fail, the node will be marked as unhealthy, and the unhealthy node will be ignored by APISIX's load balancer and cannot receive requests; if For an unhealthy node, if M consecutive probes are successful, the node will be re-marked as healthy and can be proxied.

Passive check#

Passive health check refers to judging whether the corresponding upstream node is healthy by judging the response status of the request forwarded from APISIX to the upstream node. Compared with the active health check, the passive health check method does not need to initiate additional probes, but it cannot sense the node status in advance, and there may be a certain amount of failed requests.

If N consecutive requests to a healthy node A fail, the node will be marked as unhealthy.

note

Since unhealthy nodes cannot receive requests, nodes cannot be re-marked as healthy using the passive health check strategy alone, so combining the active health check strategy is usually necessary.

tip
  • We only start the health check when the upstream is hit by a request. There won't be any health check if an upstream is configured but isn't in used.
  • If there is no healthy node can be chosen, we will continue to access the upstream.
  • We won't start the health check when the upstream only has one node, as we will access it whether this unique node is healthy or not.

Configuration instructions#

NameConfiguration typeValue typeValid valuesDefaultDescription
upstream.checks.active.typeActive checkstringhttp https tcphttpThe type of active check.
upstream.checks.active.timeoutActive checkinteger1The timeout period of the active check (unit: second).
upstream.checks.active.concurrencyActive checkinteger10The number of targets to be checked at the same time during the active check.
upstream.checks.active.http_pathActive checkstring/The HTTP request path that is actively checked.
upstream.checks.active.hostActive checkstring${upstream.node.host}The hostname of the HTTP request actively checked.
upstream.checks.active.portActive checkinteger1 to 65535${upstream.node.port}The host port of the HTTP request that is actively checked.
upstream.checks.active.https_verify_certificateActive checkbooleantrueActive check whether to check the SSL certificate of the remote host when HTTPS type checking is used.
upstream.checks.active.req_headersActive checkarray[]Active check When using HTTP or HTTPS type checking, set additional request header information.
upstream.checks.active.healthy.intervalActive check (healthy node)integer>= 11Active check (healthy node) check interval (unit: second)
upstream.checks.active.healthy.http_statusesActive check (healthy node)array200 to 599[200, 302]Active check (healthy node) HTTP or HTTPS type check, the HTTP status code of the healthy node.
upstream.checks.active.healthy.successesActive check (healthy node)integer1 to 2542Active check (healthy node) determine the number of times a node is healthy.
upstream.checks.active.unhealthy.intervalActive check (unhealthy node)integer>= 11Active check (unhealthy node) check interval (unit: second)
upstream.checks.active.unhealthy.http_statusesActive check (unhealthy node)array200 to 599[429, 404, 500, 501, 502, 503, 504, 505]Active check (unhealthy node) HTTP or HTTPS type check, the HTTP status code of the non-healthy node.
upstream.checks.active.unhealthy.http_failuresActive check (unhealthy node)integer1 to 2545Active check (unhealthy node) HTTP or HTTPS type check, determine the number of times that the node is not healthy.
upstream.checks.active.unhealthy.tcp_failuresActive check (unhealthy node)integer1 to 2542Active check (unhealthy node) TCP type check, determine the number of times that the node is not healthy.
upstream.checks.active.unhealthy.timeoutsActive check (unhealthy node)integer1 to 2543Active check (unhealthy node) to determine the number of timeouts for unhealthy nodes.
upstream.checks.passive.typePassive checkstringhttp https tcphttpThe type of passive check.
upstream.checks.passive.healthy.http_statusesPassive check (healthy node)array200 to 599[200, 201, 202, 203, 204, 205, 206, 207, 208, 226, 300, 301, 302, 303, 304, 305, 306, 307, 308]Passive check (healthy node) HTTP or HTTPS type check, the HTTP status code of the healthy node.
upstream.checks.passive.healthy.successesPassive check (healthy node)integer0 to 2545Passive checks (healthy node) determine the number of times a node is healthy.
upstream.checks.passive.unhealthy.http_statusesPassive check (unhealthy node)array200 to 599[429, 500, 503]Passive check (unhealthy node) HTTP or HTTPS type check, the HTTP status code of the non-healthy node.
upstream.checks.passive.unhealthy.tcp_failuresPassive check (unhealthy node)integer0 to 2542Passive check (unhealthy node) When TCP type is checked, determine the number of times that the node is not healthy.
upstream.checks.passive.unhealthy.timeoutsPassive check (unhealthy node)integer0 to 2547Passive checks (unhealthy node) determine the number of timeouts for unhealthy nodes.
upstream.checks.passive.unhealthy.http_failuresPassive check (unhealthy node)integer0 to 2545Passive check (unhealthy node) The number of times that the node is not healthy during HTTP or HTTPS type checking.

Configuration example#

You can enable health checks in routes via the Admin API:

curl http://127.0.0.1:9180/apisix/admin/routes/1 -H 'X-API-KEY: edd1c9f034335f136f87ad84b625c8f1' -X PUT -d '
{
"uri": "/index.html",
"plugins": {
"limit-count": {
"count": 2,
"time_window": 60,
"rejected_code": 503,
"key": "remote_addr"
}
},
"upstream": {
"nodes": {
"127.0.0.1:1980": 1,
"127.0.0.1:1970": 1
},
"type": "roundrobin",
"retries": 2,
"checks": {
"active": {
"timeout": 5,
"http_path": "/status",
"host": "foo.com",
"healthy": {
"interval": 2,
"successes": 1
},
"unhealthy": {
"interval": 1,
"http_failures": 2
},
"req_headers": ["User-Agent: curl/7.29.0"]
},
"passive": {
"healthy": {
"http_statuses": [200, 201],
"successes": 3
},
"unhealthy": {
"http_statuses": [500],
"http_failures": 3,
"tcp_failures": 3
}
}
}
}
}'

If APISIX detects an unhealthy node, the following logs will be output in the error log:

enabled healthcheck passive while logging request
failed to receive status line from 'nil (127.0.0.1:1980)': closed
unhealthy TCP increment (1/2) for '(127.0.0.1:1980)'
failed to receive status line from 'nil (127.0.0.1:1980)': closed
unhealthy TCP increment (2/2) for '(127.0.0.1:1980'
tip

To observe the above log information, you need to adjust the error log level to info.

The health check status can be fetched via GET /v1/healthcheck in Control API.


curl http://127.0.0.1:9090/v1/healthcheck/upstreams/healthycheck -s | jq .