Docker Compose - A gentle introduction with WordPress

Docker Compose is a orchestration tool for multi-container Docker applications.

We can configure our application's services via a single command to create and start all the services from our configuration using a Compose file. In other words, by using Docker Compose we can orchestrate processes of Docker containers such as starting up, shutting down, and setting up intra-container linking and volumes.

Using Compose is basically a three-step process:

1. Define app's environment with a Dockerfile so it can be reproduced anywhere.
2. Define the services that make up an app in docker-compose.yml so they can be run together in an isolated environment.
3. Run docker-compose up and Compose will start and run the entire app.

Throughout this, we'll work on Ubuntu 14.04.

In this section, we'll play with a simple test using Docker Compose just to get the taste of it.

Because we'll launch just one container, the test won't demonstrate one of the main features of Docker Compose: up and down a group of Docker containers all at the same time.

The docker-compose command works on a per-directory basis. So, we just make one directory for each container and one docker-compose.yml file for each container inside its directory. In that way, we can have multiple groups of Docker containers running on one machine.

We'll be working on a virtual environment (python 2.7):

$ virtualenv venv
$ source venv/bin/activate
(venv) $

Install python-pip:

$ sudo apt-get -y install python-pip

Install Docker Compose:

$ sudo pip install docker-compose

~/hello-world/docker-compose.yml:

my-test:
  image: hello-world

The first line is the container name while the second line specifies the container image which will be downloaded from the Docker Hub repository.

$ docker-compose up
Creating helloworld_my-test_1
Attaching to helloworld_my-test_1
my-test_1  | 
my-test_1  | Hello from Docker.
my-test_1  | This message shows that your installation appears to be working correctly.
...

The output then explains what Docker is doing with Docker Hub, Docker daemon, and Docker client:

1. The Docker client contacted the Docker daemon.
2. The Docker daemon pulled the "hello-world" image from the Docker Hub.
3. The Docker daemon created a new container from that image which runs the executable that produces the output above.
4. The Docker daemon streamed that output to the Docker client, which sent it to our terminal.

In the following sections, we'll deal with a real-world example of using Docker Compose to install an WordPress application. We'll install MariaDB as well.

Since WordPress app normally runs on a LAMP stack, we need Linux, Apache, MySQL/MariaDB, and PHP.

The official WordPress Docker image provides Apache and PHP for us but not MariaDB which we need to take care of by ourselves.

We need to tell Docker Compose to start a new container called wordpress and download the wordpress image from the Docker Hub.

~/wordpress/docker-compose.yml:

wordpress:
  image: wordpress

To bring up the image:

(venv)~/wordpress$ docker-compose up

At the end of the download process, we get complains like this:

...
wordpress_1  | error: missing required WORDPRESS_DB_PASSWORD environment variable
wordpress_1  |   Did you forget to -e WORDPRESS_DB_PASSWORD=... ?
wordpress_1  | 
wordpress_1  |   (Also of interest might be WORDPRESS_DB_USER and WORDPRESS_DB_NAME.)
wordpress_wordpress_1 exited with code 1

It tells us our wordpress needs db.

We should define a new container called wordpress_db and tell Docker to use the mariadb image from the Docker Hub.

To add the MariaDB image to the group, let's modify our ~/wordpress/docker-compose.yml :

wordpress:
  image: wordpress
  links:
    - wordpress_db:mysql
wordpress_db:
  image: mariadb

With the modification, we'll have two containers: wordpress container and wordpress_db container.

We're telling our wordpress container to link our wordpress_db container into the wordpress container and call it mysql.

So, inside the wordpress container the hostname mysql will be forwarded to our wordpress_db container.

Let's run docker-compose up again:

(venv)~/wordpress$ docker-compose up
...
ERROR: for wordpress  Cannot start service wordpress: Cannot start container d14451708c365e5c0862194e6585620569f06caaf0fc8c226a0a44a332adf70a: Cannot link to a non running container: /wordpress_wordpress_db_1 AS /wordpress_wordpress_1/mysql
ERROR: Encountered errors while bringing up the project.

Still we see that we're not quite there yet though. More work needs to be done.

It looks like just linking the two containers isn't quite enough: we need to set the MYSQL_ROOT_PASSWORD variable.

wordpress:
  image: wordpress
  links:
    - wordpress_db:mysql
  ports:
    - 8888:80
wordpress_db:
  image: mariadb
  environment:
    MYSQL_ROOT_PASSWORD: mysql-root-password

In 'port' section, the first port number is the host port number, and the second port number is the container port. The port configuration forwards requests on port 8888 of the host to the default web server port 80 inside the container.

(venv)~/wordpress$ docker-compose up -d
Starting wordpress_wordpress_db_1
Starting wordpress_wordpress_1
(venv)~/wordpress$

This time, we run it with the -d option, which will tell docker-compose to run the containers in the background as a service.

Open up a web browser (localhost:8888):

Stop all the Docker containers with the following command:

$ docker-compose stop

Instead of using the legacy link for communications between containers, we can use networks as shown in Docker Networks - Bridge.

Docker & K8s

1. Docker install on Amazon Linux AMI
2. Docker install on EC2 Ubuntu 14.04
3. Docker container vs Virtual Machine
4. Docker install on Ubuntu 14.04
5. Docker Hello World Application
6. Nginx image - share/copy files, Dockerfile
7. Working with Docker images : brief introduction
8. Docker image and container via docker commands (search, pull, run, ps, restart, attach, and rm)
9. More on docker run command (docker run -it, docker run --rm, etc.)
10. Docker Networks - Bridge Driver Network
11. Docker Persistent Storage
12. File sharing between host and container (docker run -d -p -v)
13. Linking containers and volume for datastore
14. Dockerfile - Build Docker images automatically I - FROM, MAINTAINER, and build context
15. Dockerfile - Build Docker images automatically II - revisiting FROM, MAINTAINER, build context, and caching
16. Dockerfile - Build Docker images automatically III - RUN
17. Dockerfile - Build Docker images automatically IV - CMD
18. Dockerfile - Build Docker images automatically V - WORKDIR, ENV, ADD, and ENTRYPOINT
19. Docker - Apache Tomcat
20. Docker - NodeJS
21. Docker - NodeJS with hostname
22. Docker Compose - NodeJS with MongoDB
23. Docker - Prometheus and Grafana with Docker-compose
24. Docker - StatsD/Graphite/Grafana
25. Docker - Deploying a Java EE JBoss/WildFly Application on AWS Elastic Beanstalk Using Docker Containers
26. Docker : NodeJS with GCP Kubernetes Engine
27. Docker : Jenkins Multibranch Pipeline with Jenkinsfile and Github
28. Docker : Jenkins Master and Slave
29. Docker - ELK : ElasticSearch, Logstash, and Kibana
30. Docker - ELK 7.6 : Elasticsearch on Centos 7
31. Docker - ELK 7.6 : Filebeat on Centos 7
32. Docker - ELK 7.6 : Logstash on Centos 7
33. Docker - ELK 7.6 : Kibana on Centos 7
34. Docker - ELK 7.6 : Elastic Stack with Docker Compose
35. Docker - Deploy Elastic Cloud on Kubernetes (ECK) via Elasticsearch operator on minikube
36. Docker - Deploy Elastic Stack via Helm on minikube
37. Docker Compose - A gentle introduction with WordPress
38. Docker Compose - MySQL
39. MEAN Stack app on Docker containers : micro services
40. MEAN Stack app on Docker containers : micro services via docker-compose
41. Docker Compose - Hashicorp's Vault and Consul Part A (install vault, unsealing, static secrets, and policies)
42. Docker Compose - Hashicorp's Vault and Consul Part B (EaaS, dynamic secrets, leases, and revocation)
43. Docker Compose - Hashicorp's Vault and Consul Part C (Consul)
44. Docker Compose with two containers - Flask REST API service container and an Apache server container
45. Docker compose : Nginx reverse proxy with multiple containers
46. Docker & Kubernetes : Envoy - Getting started
47. Docker & Kubernetes : Envoy - Front Proxy
48. Docker & Kubernetes : Ambassador - Envoy API Gateway on Kubernetes
49. Docker Packer
50. Docker Cheat Sheet
51. Docker Q & A #1
52. Kubernetes Q & A - Part I
53. Kubernetes Q & A - Part II
54. Docker - Run a React app in a docker
55. Docker - Run a React app in a docker II (snapshot app with nginx)
56. Docker - NodeJS and MySQL app with React in a docker
57. Docker - Step by Step NodeJS and MySQL app with React - I
58. Installing LAMP via puppet on Docker
59. Docker install via Puppet
60. Nginx Docker install via Ansible
61. Apache Hadoop CDH 5.8 Install with QuickStarts Docker
62. Docker - Deploying Flask app to ECS
63. Docker Compose - Deploying WordPress to AWS
64. Docker - WordPress Deploy to ECS with Docker-Compose (ECS-CLI EC2 type)
65. Docker - WordPress Deploy to ECS with Docker-Compose (ECS-CLI Fargate type)
66. Docker - ECS Fargate
67. Docker - AWS ECS service discovery with Flask and Redis
68. Docker & Kubernetes : minikube
69. Docker & Kubernetes 2 : minikube Django with Postgres - persistent volume
70. Docker & Kubernetes 3 : minikube Django with Redis and Celery
71. Docker & Kubernetes 4 : Django with RDS via AWS Kops
72. Docker & Kubernetes : Kops on AWS
73. Docker & Kubernetes : Ingress controller on AWS with Kops
74. Docker & Kubernetes : HashiCorp's Vault and Consul on minikube
75. Docker & Kubernetes : HashiCorp's Vault and Consul - Auto-unseal using Transit Secrets Engine
76. Docker & Kubernetes : Persistent Volumes & Persistent Volumes Claims - hostPath and annotations
77. Docker & Kubernetes : Persistent Volumes - Dynamic volume provisioning
78. Docker & Kubernetes : DaemonSet
79. Docker & Kubernetes : Secrets
80. Docker & Kubernetes : kubectl command
81. Docker & Kubernetes : Assign a Kubernetes Pod to a particular node in a Kubernetes cluster
82. Docker & Kubernetes : Configure a Pod to Use a ConfigMap
83. AWS : EKS (Elastic Container Service for Kubernetes)
84. Docker & Kubernetes : Run a React app in a minikube
85. Docker & Kubernetes : Minikube install on AWS EC2
86. Docker & Kubernetes : Cassandra with a StatefulSet
87. Docker & Kubernetes : Terraform and AWS EKS
88. Docker & Kubernetes : Pods and Service definitions
89. Docker & Kubernetes : Service IP and the Service Type
90. Docker & Kubernetes : Kubernetes DNS with Pods and Services
91. Docker & Kubernetes : Headless service and discovering pods
92. Docker & Kubernetes : Scaling and Updating application
93. Docker & Kubernetes : Horizontal pod autoscaler on minikubes
94. Docker & Kubernetes : From a monolithic app to micro services on GCP Kubernetes
95. Docker & Kubernetes : Rolling updates
96. Docker & Kubernetes : Deployments to GKE (Rolling update, Canary and Blue-green deployments)
97. Docker & Kubernetes : Slack Chat Bot with NodeJS on GCP Kubernetes
98. Docker & Kubernetes : Continuous Delivery with Jenkins Multibranch Pipeline for Dev, Canary, and Production Environments on GCP Kubernetes
99. Docker & Kubernetes : NodePort vs LoadBalancer vs Ingress
100. Docker & Kubernetes : MongoDB / MongoExpress on Minikube
101. Docker & Kubernetes : Load Testing with Locust on GCP Kubernetes
102. Docker & Kubernetes : MongoDB with StatefulSets on GCP Kubernetes Engine
103. Docker & Kubernetes : Nginx Ingress Controller on Minikube
104. Docker & Kubernetes : Setting up Ingress with NGINX Controller on Minikube (Mac)
105. Docker & Kubernetes : Nginx Ingress Controller for Dashboard service on Minikube
106. Docker & Kubernetes : Nginx Ingress Controller on GCP Kubernetes
107. Docker & Kubernetes : Kubernetes Ingress with AWS ALB Ingress Controller in EKS
108. Docker & Kubernetes : Setting up a private cluster on GCP Kubernetes
109. Docker & Kubernetes : Kubernetes Namespaces (default, kube-public, kube-system) and switching namespaces (kubens)
110. Docker & Kubernetes : StatefulSets on minikube
111. Docker & Kubernetes : RBAC
112. Docker & Kubernetes Service Account, RBAC, and IAM
113. Docker & Kubernetes - Kubernetes Service Account, RBAC, IAM with EKS ALB, Part 1
114. Docker & Kubernetes : Helm Chart
115. Docker & Kubernetes : My first Helm deploy
116. Docker & Kubernetes : Readiness and Liveness Probes
117. Docker & Kubernetes : Helm chart repository with Github pages
118. Docker & Kubernetes : Deploying WordPress and MariaDB with Ingress to Minikube using Helm Chart
119. Docker & Kubernetes : Deploying WordPress and MariaDB to AWS using Helm 2 Chart
120. Docker & Kubernetes : Deploying WordPress and MariaDB to AWS using Helm 3 Chart
121. Docker & Kubernetes : Helm Chart for Node/Express and MySQL with Ingress
122. Docker & Kubernetes : Deploy Prometheus and Grafana using Helm and Prometheus Operator - Monitoring Kubernetes node resources out of the box
123. Docker & Kubernetes : Deploy Prometheus and Grafana using kube-prometheus-stack Helm Chart
124. Docker & Kubernetes : Istio (service mesh) sidecar proxy on GCP Kubernetes
125. Docker & Kubernetes : Istio on EKS
126. Docker & Kubernetes : Istio on Minikube with AWS EC2 for Bookinfo Application
127. Docker & Kubernetes : Deploying .NET Core app to Kubernetes Engine and configuring its traffic managed by Istio (Part I)
128. Docker & Kubernetes : Deploying .NET Core app to Kubernetes Engine and configuring its traffic managed by Istio (Part II - Prometheus, Grafana, pin a service, split traffic, and inject faults)
129. Docker & Kubernetes : Helm Package Manager with MySQL on GCP Kubernetes Engine
130. Docker & Kubernetes : Deploying Memcached on Kubernetes Engine
131. Docker & Kubernetes : EKS Control Plane (API server) Metrics with Prometheus
132. Docker & Kubernetes : Spinnaker on EKS with Halyard
133. Docker & Kubernetes : Continuous Delivery Pipelines with Spinnaker and Kubernetes Engine
134. Docker & Kubernetes : Multi-node Local Kubernetes cluster : Kubeadm-dind (docker-in-docker)
135. Docker & Kubernetes : Multi-node Local Kubernetes cluster : Kubeadm-kind (k8s-in-docker)
136. Docker & Kubernetes : nodeSelector, nodeAffinity, taints/tolerations, pod affinity and anti-affinity - Assigning Pods to Nodes
137. Docker & Kubernetes : Jenkins-X on EKS
138. Docker & Kubernetes : ArgoCD App of Apps with Heml on Kubernetes
139. Docker & Kubernetes : ArgoCD on Kubernetes cluster
140. Docker & Kubernetes : GitOps with ArgoCD for Continuous Delivery to Kubernetes clusters (minikube) - guestbook