Step 4: Add additional Services

Let’s add another service to our project. Wordpress stores most of its data in the database, which can slow the system down if the database is hit frequently. We will improve performance by using memory caching. The first time a request is made, the data is pulled from the database and stored in memory. If the same data is accessed again, the caching service uses the copy in memory.

Redis and Memcached are both in-memory data storage systems. Memcached is a high-performance distributed memory cache service, and Redis is an open-source key-value store. Similar to Memcached, Redis stores most of the data in memory. These services keep data in memory because it is faster than reading it from the database. We’ll add Redis from Docker Hub.

Install Redis Server

Tip

Students often times have mistakes in their YAML file because of incorrect spaces. You can validate your docker-compose.yml file using website YAML Lint.

  1. Add the Redis service to our Wordpress docker-compose.yml file.

    1. Edit file docker-compose.yml.

    2. Add a new section called redis between sections db and wordpress.

    redis:
  image: redis
  restart: always

  2. We need to link it to Wordpress so it can make use it.

    1. Add the reference to redis under the depends_on property.

    wordpress:
  depends_on:
    - db
    - redis

  3. Let’s restart the project and configure Redis.

    • We can do this in a one-line command

    • Use && is to separate the commands

    docker-compose down && docker-compose up -d
    Output
    root@vps298933:~/wordpress-docker# docker-compose down && docker-compose up -d
Stopping wordpressdocker_wordpress_1 ... done
Stopping wordpressdocker_db_1        ... done
Removing wordpressdocker_wordpress_1 ... done
Removing wordpressdocker_db_1        ... done
Removing network wordpressdocker_default
Creating network "wordpressdocker_default" with the default driver
Pulling redis (redis:latest)...
latest: Pulling from library/redis
27833a3ba0a5: Already exists
cde8019a4b43: Pull complete
97a473b37fb2: Pull complete
c6fe0dfbb7e3: Pull complete
39c8f5ba1240: Pull complete
cfbdd870cf75: Pull complete
Digest: sha256:000339fb57e0ddf2d48d72f3341e47a8ca3b1beae9bdcb25a96323095b72a79b
Status: Downloaded newer image for redis:latest
Creating wordpressdocker_redis_1 ...
Creating wordpressdocker_db_1 ...
Creating wordpressdocker_redis_1
Creating wordpressdocker_db_1 ... done
Creating wordpressdocker_wordpress_1 ...
Creating wordpressdocker_wordpress_1 ... done
root@vps298933:~/wordpress-docker#

    • As you can see, Docker Compose downloaded image redis:latest and then created a new container called wordpressdocker_redis_1.

    • We can’t test Redis easily because we did not configure an outside port. You can see that it is running on an internal port only. Other Docker containers can access it, but we can’t.

    Output
    root@vps298933:~/wordpress-docker# docker ps
CONTAINER ID        IMAGE                COMMAND                  CREATED             STATUS              PORTS                     NAMES
61dc491c1749        wordpress:latest     "docker-entrypoint.s…"   12 seconds ago      Up 10 seconds       0.0.0.0:20851->80/tcp      wordpressdocker_wordpress_1
6f5367faa44c        mariadb              "docker-entrypoint.s…"   13 seconds ago      Up 12 seconds       3306/tcp                   wordpressdocker_db_1
aa6c82e67ffc        redis                "docker-entrypoint.s…"   13 seconds ago      Up 12 seconds       6379/tcp                   wordpressdocker_redis_1
2175f0a86466        nextcloud            "/entrypoint.sh apac…"   7 days ago          Up 6 days           0.0.0.0:20850->80/tcp      condescending_agnesi
root@vps298933:~/wordpress-docker#

Testing Redis on Docker

You can explore this more on your own, but you can test the Redis server running on container wordpressdocker_redis_1 if you know the IP address of the specific container.

The specific commands are:

redis-cli -h <IPAddress> ping
redis-cli -h <IPAddress> info

  1. Locate the IP address of the container using docker inspect:

    docker inspect wordpressdocker_redis_1

    Note

    Your IP address will be different. The IPAddress key value pair in the example below i:

    "IPAddress": "192.168.208.2",
    IP Address of Container
    root@vps298933:~/wordpress-docker# docker inspect wordpressdocker_redis_1
[
    {
        "Id": "913ff74dd94c5a00f9d54b7c2e7a00ad8700322ccc02c5b84339102d1915ba9b",
        "Created": "2019-03-30T07:12:32.603181563Z",
        "Path": "docker-entrypoint.sh",
        "Args": [
            "redis-server"
        ],
        "State": {
            "Status": "running",
            "Running": true,
.
.
.
                    "NetworkID": "9ed37a99240fdadb14fbcce1be2ca1f469f286daa8fff87826c26932756493b8",
                    "EndpointID": "f80cc3e39ef2f73f6c5ecdfa4690d2b2ce3691586a2c0a3a2ee9cf9cddea3908",
                    "Gateway": "192.168.208.1",
                    "IPAddress": "192.168.208.2",
                    "IPPrefixLen": 20,
                    "IPv6Gateway": "",
                    "GlobalIPv6Address": "",
                    "GlobalIPv6PrefixLen": 0,
                    "MacAddress": "02:42:c0:a8:d0:02",
                    "DriverOpts": null
                }
            }
        }
    }
]

root@vps298933:~/wordpress-docker# ping 192.168.208.1
PING 192.168.208.1 (192.168.208.1) 56(84) bytes of data.
64 bytes from 192.168.208.1: icmp_seq=1 ttl=64 time=0.063 ms
64 bytes from 192.168.208.1: icmp_seq=2 ttl=64 time=0.073 ms
^C
--- 192.168.208.1 ping statistics ---
2 packets transmitted, 2 received, 0% packet loss, time 1023ms
rtt min/avg/max/mdev = 0.063/0.068/0.073/0.005 ms
root@vps298933:~/wordpress-docker#
root@vps298933:~/wordpress-docker# redis-cli -h 192.168.208.1 ping
Could not connect to Redis at 192.168.208.1:6379: Connection refused
root@vps298933:~/wordpress-docker# ping 192.168.208.2
PING 192.168.208.2 (192.168.208.2) 56(84) bytes of data.
64 bytes from 192.168.208.2: icmp_seq=1 ttl=64 time=0.181 ms
64 bytes from 192.168.208.2: icmp_seq=2 ttl=64 time=0.091 ms
^C
--- 192.168.208.2 ping statistics ---
2 packets transmitted, 2 received, 0% packet loss, time 1030ms
rtt min/avg/max/mdev = 0.091/0.136/0.181/0.045 ms
root@vps298933:~/wordpress-docker# redis-cli -h 192.168.208.2 ping
PONG
root@vps298933:~/wordpress-docker# redis-cli -h 192.168.208.2 info clients
# Clients
connected_clients:1
client_recent_max_input_buffer:32774
client_recent_max_output_buffer:0
blocked_clients:0
root@vps298933:~/wordpress-docker#

  2. Now we can test Redis using redis-cli because Redis is available on port 6379. But, we need to install the package first.

    apt install -y redis-tools
    Output
    root@vps298933:~/wordpress-docker# redis-cli ping

Command 'redis-cli' not found, but can be installed with:

apt install redis-tools

root@vps298933:~/wordpress-docker#
root@vps298933:~/wordpress-docker# apt install redis-tools -y
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following additional packages will be installed:
  libjemalloc1
Suggested packages:
  ruby-redis
The following NEW packages will be installed:
  libjemalloc1 redis-tools
0 upgraded, 2 newly installed, 0 to remove and 0 not upgraded.
Need to get 599 kB of archives.
After this operation, 2,835 kB of additional disk space will be used.
Get:1 http://nova.clouds.archive.ubuntu.com/ubuntu bionic/universe amd64 libjemalloc1 amd64 3.6.0-11 [82.4 kB]
Get:2 http://nova.clouds.archive.ubuntu.com/ubuntu bionic-updates/universe amd64 redis-tools amd64 5:4.0.9-1ubuntu0.1 [516 kB]
Fetched 599 kB in 0s (2,740 kB/s)
Selecting previously unselected package libjemalloc1.
(Reading database ... 132723 files and directories currently installed.)
Preparing to unpack .../libjemalloc1_3.6.0-11_amd64.deb ...
Unpacking libjemalloc1 (3.6.0-11) ...
Selecting previously unselected package redis-tools.
Preparing to unpack .../redis-tools_5%3a4.0.9-1ubuntu0.1_amd64.deb ...
Unpacking redis-tools (5:4.0.9-1ubuntu0.1) ...
Setting up libjemalloc1 (3.6.0-11) ...
Processing triggers for libc-bin (2.27-3ubuntu1) ...
Processing triggers for man-db (2.8.3-2ubuntu0.1) ...
Setting up redis-tools (5:4.0.9-1ubuntu0.1) ...
root@vps298933:~/wordpress-docker#

  3. First of all, let’s test the connection using ping. The expected output is pong.

    redis-cli -h IPAddress info
    Expected Output
    root@vps298933:~/wordpress-docker# redis-cli -h 172.22.0.3 ping
PONG
root@vps298933:~/wordpress-docker#

    Error

    • You will get a Connection refused message if something is misconfigured or if you have the wrong IP address, such as trying to use localhost.

    Output
    root@vps298933:~/wordpress-docker# redis-cli ping
Could not connect to Redis at 127.0.0.1:6379: Connection refused

  4. We can use the redis-cli tool to look at all of the information available.

    redis-cli -h IPAddress info
    Output
    root@vps298933:~/wordpress-docker# redis-cli -h 172.22.0.3 info
# Server
redis_version:5.0.4
redis_git_sha1:00000000
redis_git_dirty:0
redis_build_id:c6d7e1572d62bb79
redis_mode:standalone
os:Linux 4.15.0-46-generic x86_64
arch_bits:64
multiplexing_api:epoll
atomicvar_api:atomic-builtin
gcc_version:6.3.0
process_id:1
run_id:21c1137b7c733b539977f3a7f6646a0b95a15654
tcp_port:6379
uptime_in_seconds:60
uptime_in_days:0
hz:10
configured_hz:10
lru_clock:10422992
executable:/data/redis-server
config_file:

# Clients
connected_clients:1
client_recent_max_input_buffer:0
client_recent_max_output_buffer:0
blocked_clients:0

# Memory
used_memory:853896
used_memory_human:833.88K
.
.
.

    • We can look at individual sections of the info that are separated by the # symbol, such as server or memory.

    redis-cli -h IPAddress info server
redis-cli -h IPAddress info memory
    Output
    root@vps298933:~/wordpress-docker# redis-cli -h 172.22.0.3 info server
# Server
redis_version:5.0.4
redis_git_sha1:00000000
redis_git_dirty:0
redis_build_id:c6d7e1572d62bb79
redis_mode:standalone
os:Linux 4.15.0-46-generic x86_64
arch_bits:64
multiplexing_api:epoll
atomicvar_api:atomic-builtin
gcc_version:6.3.0
process_id:1
run_id:21c1137b7c733b539977f3a7f6646a0b95a15654
tcp_port:6379
uptime_in_seconds:72
uptime_in_days:0
hz:10
configured_hz:10
lru_clock:10423004
executable:/data/redis-server
config_file:
root@vps298933:~/wordpress-docker#
root@vps298933:~/wordpress-docker# redis-cli -h 172.22.0.3 info memory
# Memory
used_memory:852920
used_memory_human:832.93K
used_memory_rss:4444160
used_memory_rss_human:4.24M
used_memory_peak:853896
used_memory_peak_human:833.88K
used_memory_peak_perc:99.89%
used_memory_overhead:840694
used_memory_startup:791000
used_memory_dataset:12226
used_memory_dataset_perc:19.74%
allocator_allocated:1027896
allocator_active:1220608
allocator_resident:3497984
total_system_memory:4035948544
total_system_memory_human:3.76G
used_memory_lua:37888
used_memory_lua_human:37.00K
used_memory_scripts:0
used_memory_scripts_human:0B
number_of_cached_scripts:0
maxmemory:0
maxmemory_human:0B
maxmemory_policy:noeviction
allocator_frag_ratio:1.19
allocator_frag_bytes:192712
allocator_rss_ratio:2.87
allocator_rss_bytes:2277376
rss_overhead_ratio:1.27
rss_overhead_bytes:946176
mem_fragmentation_ratio:5.62
mem_fragmentation_bytes:3653144
mem_not_counted_for_evict:0
mem_replication_backlog:0
mem_clients_slaves:0
mem_clients_normal:49694
mem_aof_buffer:0
mem_allocator:jemalloc-5.1.0
active_defrag_running:0
lazyfree_pending_objects:0