Experiencing the same issues.... Seeking expert assistance

Without some more information it can be hard to find a cause.

One cause I see a lot is Apache can get stuck if the memory limit is hit on all instances open and timeout is disabled or made really long. If ignore user exit is turned on in Wordpress or PHP it will keep running a script even if in a loop and the user leaves.

Is there any CPU spikes around the same time? You might want to install a server monitor of some kind like New Relic that will give you info on what happens when it happens.

@programmer2188

To get a better idea of how you're setup:

1). What size is your Droplet? (512MB, 1GB, 2GB, etc)

2). Is Apache, PHP, and MariaDB the only software running?

3). Since you're using WordPress, what plugins, if any, do you have installed?
3a). Are they all up-to-date?

4). When running top via SSH, what's your CPU/RAM usage during:

• Idle or Low-Traffic times; and
• Peak or High-Traffic times

@programmer2188

Honestly, that's not as many plugins as I was expecting to be honest, so the count isn't an issue. I've seen 1-2GB instances run 2-3x that without any issues.

WordPress Plugins Overall

That said, one plugin that is always a concern in my eyes is EWWW Image Optimizer Cloud. Why? It has the potential to be a resource hog, especially if you're uploading quite a few images, or if you're allowing others to. For a small WordPress instance, it's really a non-issue, but if you upload a series of images and watch top, you can see what I mean. Because of the software it requires from the web server, and the overall intensiveness of said software, it can shoot CPU usage up to the ceiling and with it, your RAM (and lack of both means processes start hanging, fighting for resources, and ultimately crash when they can't get what they need).

While I understand the utility of the plugin, you're far better offer simply running them on your own prior to uploading them. Services such as the below are far better options:

https://compressor.io/
https://tinypng.com/

and on the commercial end:

https://kraken.io/

WordPress Plugins: W3 Total Cache

What are you setup to use? Are you using OpCode Caching, Memcached, Redis, File, or something else?

Optimizing MySQL

Login to SSH and grab your current MySQL configuration from /etc/mysql/my.cnf. While it normally takes a pretty busy site to bog dog even the most basic MySQL configuration, there's always one or two things we can tweak to speed things up -- or test.

Drop Apache, Use NGINX

Unless you're familiar with NGINX or the CLI, this is more of a last-ditch move. NGINX is ultimately more performant as is PHP-FPM over the default PHP module used by Apache. Using W3TC with NGINX, however, does require a little more love than it does with Apache, but it's really worth it.

What may cause high loads on Apache often results in seemingly reduced and low loads with NGINX.

@programmer2188

W3TC will generate a file when it detects NGINX instead of Apache and you'll essentially copy/paste the contents of that file in to your NGINX server block, then restart NGINX. The extra part I mentioned is because you have to manually do this anytime you make changes that would extend or remove any portion of the server block code that W3TC generates.

W3TC will generate changes made to your .htaccess file on the fly as long as it has the permissions to write to it. NGINX doesn't work that way since all of your configuration goes inside the server block for your domain.

That being said, NGINX + PHP-FPM, in my experience, is more performant than Apache + mod_php or similar. It can be used as a standard HTTP server, reverse proxy, caching proxy, etc. Also, should the need arise, you can actually separate NGINX from PHP-FPM and run them on their own servers. You would then configure NGINX to proxy the request to the PHP-FPM server. I actually just setup testing for that exact configuration.

MySQL Configuration

First off, before modifying your my.cnf file, make a backup copy:

cp /etc/mysql/my.cnf /usr/local/src/my.cnf

Verify the above backup is a valid copy and then shutdown MySQL:

service mysql stop

Then simply delete the existing file, create a new one, and then paste the contents below in.

sudo rm -rf /etc/mysql/my.cnf \
&& nano /etc/mysql/my.cnf

[mysql]
max_allowed_packet = 32M

[mysqld]
local-infile=0
datadir=/var/lib/mysql
socket=/var/lib/mysql/mysql.sock
symbolic-links=0

back_log = 75
max_connections = 300
key_buffer_size = 32M
myisam_sort_buffer_size = 32M
myisam_max_sort_file_size = 2048M
join_buffer_size = 64K
read_buffer_size = 64K
sort_buffer_size = 128K
table_definition_cache = 4096
table_open_cache = 2048
thread_cache_size = 64
wait_timeout = 1800
connect_timeout = 10
tmp_table_size = 32M
max_heap_table_size = 32M
max_allowed_packet = 32M
max_seeks_for_key = 1000
group_concat_max_len = 1024
max_length_for_sort_data = 1024
net_buffer_length = 16384
max_connect_errors = 100000
concurrent_insert = 2
read_rnd_buffer_size = 256K
bulk_insert_buffer_size = 8M
query_cache_limit = 512K
query_cache_size = 16M
query_cache_type = 1
query_cache_min_res_unit = 2K
query_prealloc_size = 262144
query_alloc_block_size = 65536
transaction_alloc_block_size = 8192
transaction_prealloc_size = 4096
default-storage-engine = InnoDB

log_warnings=1
slow_query_log=0
long_query_time=1
slow_query_log_file=/var/lib/mysql/slowq.log
log-error=/var/log/mysqld.log

innodb_large_prefix=1
innodb_purge_threads=1
innodb_doublewrite = 1

innodb_file_per_table = 1
innodb_open_files = 1000
innodb_data_file_path= ibdata1:10M:autoextend
innodb_buffer_pool_size = 48M
innodb_additional_mem_pool_size = 32M

innodb_log_files_in_group = 2
innodb_log_file_size = 64M
innodb_log_buffer_size = 8M
innodb_flush_log_at_trx_commit = 2
innodb_thread_concurrency = 0
innodb_lock_wait_timeout=50
#innodb_flush_method = O_DIRECT
innodb_support_xa=1

# 200 * # DISKS
innodb_io_capacity = 100
innodb_read_io_threads = 2
innodb_write_io_threads = 2

[mysqld_safe]
log-error=/var/log/mariadb/mariadb.log
pid-file=/var/run/mariadb/mariadb.pid

[mysqldump]
quick
max_allowed_packet = 32M

[myisamchk] 
key_buffer = 32M 
sort_buffer = 16M
read_buffer = 16M
write_buffer = 16M

[mysqlhotcopy]
interactive-timeout

Now start MySQL:

service mysql start

This is a bare minimum setup that should perform well for the time being. It enables query caching and provides tweaks to common configuration.

You shouldn't run in to any issues with that setup as long as you're running an up to date version of MySQL or MariaDB (a drop-in replacement for MySQL). If you do, that's why we created a backup so that we can revert back without issue.

If you do hit a snag, make sure to copy the error and paste it in a reply.