Docker Mastery: Section 9 - Healthchecks in Dockerfiles

• section9-80, 81

Udemy

• Docker Mastery: with Kubernetes +Swarm from a Docker Captain

• GitHub: udemy-docker-mastery

• 講師的YouTube

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Docker Healthchecks

• HEALTHCHECK was added in 1.12
• Supported in Dockerfile, Compose YAML, docker run, and Swarm Services
  • 老師強烈鼓勵在開發的時候，使用 Healthcheck cmd :)
• Docker engine will exec’s the command in the container
  • e.g curl localhost
• It expects exit 0 (ok) or exit 1 (Error)
• Three container states: starting, healthy, unhealthy
• Much better then “is binary still running?”
• Not a external monitoring replacement
• Healthcheck status shows up in docker contaienr ls
• Check last 5 healthchecks with docker container inspect
• Docker run does nothing with healthchecks
• Services will replace tasks if they fail healthcheck
• Service updates wait for them before continuing

Healthcheck Docker Run Example

• Adding Healthchecks in run time

docker run \
   --health-cmd="curl -f localhost:9200/_cluster/health || false" \
   --health-interval=5s \
   --health-retries=3 \
   --health-timeout=2s \
   --health-start-period=15s \
   elasticsearch:2

Healthcheck Dockerfile Examples

• Options for healthcheck command
  • --interval=DURATION (default: 30s)
  • --timeout=DURATION (default: 30s)
  • --start-period=DURATION (default: 0s) (17.09+)
  • --retries=N (default: 3)
• Basic command using default options
  • HEALTHCHECK curl -f http://localhost/ || false
• Custom options with the command

    HEALTHCHECK --timeout=2s --interval=3s --retries=3 \
       CMD curl -f http://localhost/ || exit 1
  

Healthchekc in Nginx Dockerfile

• Static website running in Nginx, just test default URL

FROM nginx:1.13
HEALTHCHECK --interval=30s --timeout=3s \
   CMD  curl -f http://localhost/ || exit 1 

Healthcheck in PHP Nginx Dockerfile

• PHP-FPM running behind Nginx, test the Nginx and FPM status URLs

FROM your-nginx-php-fpm-combo-image

# don't do this if php-fpm is another container 
# must enable php-fpm ping/status in pool.ini
# must forward /ping and /status urls from nginx to php-fpm

HEALTHCHECK --interval-5s --timeout=3s \
   CMD curl -f http://localhost/ping || exit 1

Healthcheck in postgres Dockerfile

• Use a PostgreSQL utility to test for ready state

FROM postgres

# specify real user with -U to prevent errors in log

HEALTHCHECK --interval=5s --timeout=3s \
   CMD pg_isready -U postgres || exit 1

Healthcheck in Compose/Stack Files

version: "2.1" #(minimum for healthchekcs)
servcies:
  web:
    image: nginx
    healthcheck:
      test: ["CMD", "curl", "-f", "http://localhost"]
      interval: 1m30s
      timeout: 10s
      retries: 3
      start_period: 1m # version 3.4 minimum

Healthcheck Example:

• docker container run --name p1 -d postgres

   PS E:\Udemy\Docker Mastery\udemy-docker-mastery\healthcheck-1> docker container run --name p1 -d postgres                     
   2101d72fb70fbe48c9f688794ef53ddbb00833c251d8d0a12f17b0cbbe1c61d4
  

• docker container run --name p2 -d --health-cmd="pg_isready -U postgres || exit 1" postgres
  • docker contaienr ls 看 contaienr 狀況
  • 超酷的拉～　可以看到健不健康　ＸＤ

  PS E:\Udemy\Docker Mastery\udemy-docker-mastery\healthcheck-1> docker container run --name p2 -d --health-cmd="pg_isready -U postgres || exit 1" postgres
  aea0766a80f1f18074915a09efd089c0db14e3e64644539567b94efa395f8bea
  PS E:\Udemy\Docker Mastery\udemy-docker-mastery\healthcheck-1> docker container ls
  CONTAINER ID        IMAGE               COMMAND                  CREATED             STATUS                            PORTS               NAMES
  aea0766a80f1        postgres            "docker-entrypoint.s…"   9 seconds ago       Up 8 seconds (health: starting)   5432/tcp            p2
  2101d72fb70f        postgres            "docker-entrypoint.s…"   3 minutes ago       Up 3 minutes                      5432/tcp            p1
  

• docker container inspect <contaeinr-name>
  • docker container inspect p2
  • 可以看到多了 "Health": {} ~~~ … “Health”: { “Status”: “healthy”, “FailingStreak”: 0, “Log”: [ { “Start”: “2020-03-10T07:03:11.576399Z”, “End”: “2020-03-10T07:03:11.7052263Z”, “ExitCode”: 0, “Output”: “/var/run/postgresql:5432 - accepting connections\n” }, { “Start”: “2020-03-10T07:03:41.7178124Z”, “End”: “2020-03-10T07:03:41.8325722Z”, “ExitCode”: 0, “Output”: “/var/run/postgresql:5432 - accepting connections\n” }, { “Start”: “2020-03-10T07:04:11.8411281Z”, “End”: “2020-03-10T07:04:11.9714451Z”, “ExitCode”: 0, “Output”: “/var/run/postgresql:5432 - accepting connections\n” }, { “Start”: “2020-03-10T07:04:41.9874807Z”, “End”: “2020-03-10T07:04:42.1301299Z”, “ExitCode”: 0, “Output”: “/var/run/postgresql:5432 - accepting connections\n” }, { “Start”: “2020-03-10T07:05:12.140623Z”, “End”: “2020-03-10T07:05:12.2619583Z”, “ExitCode”: 0, “Output”: “/var/run/postgresql:5432 - accepting connections\n” } ] } },

  … ~~~

Healthcheck: docker servcie

• docker servcie create --name p2 --health-cmd="pg_isready -U postgres || exit 1" postgres

PS E:\Udemy\Docker Mastery\udemy-docker-mastery\healthcheck-1> docker service create --name p2  --health-cmd="pg_isready -U postgres || exit 1" postgres                                                        
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overall progress: 0 out of 1 tasks                                                                      
1/1: ready