FrozenError: can't modify frozen String: ""

[firefart]

Since upgrading the apm gem to 3.3.0 the logs are filled with this message. The APM server is a elastic cloud hosted instance

web_1          | E, [2019-12-29T21:32:57.460146 #76] ERROR -- : [ElasticAPM] Couldn't establish connection to APM Server:
web_1          | "#<FrozenError: can't modify frozen String: \"\">"

[mikker]

Hi @firefart (great name 😂)

Could you try running the agent with log_level: 0 and see if you get more information?

[mikker]

And maybe provide your agent configuration if anything is set to non-default settings. Thanks!

[firefart]

Adding log_level: 0 does not give any more information it seems.

elastic_apm.yml:

# Set service name - allowed characters: 
# a-z, A-Z, 0-9, -, _ and space
# Defaults to the name of your Rails app
service_name: 'xxxx'

# Use if APM Server requires a token
#
secret_token: <%= ENV['APM_TOKEN'] %>

# Set custom APM Server URL (
# default: http://localhost:8200)
#
server_url: <%= ENV['APM_SERVER_URL'] %>

# alpine does not like the amazon certificate it seems
verify_server_cert: false

log_level: 0

Environment:
Ruby: 2.7.0 (alpine docker image)
elastic-apm 3.3.0

[firefart]

Maybe it would be a nice addition to add e.backtrace here

apm-agent-ruby/lib/elastic_apm/transport/connection/http.rb

Line 101 in b65fb99

"Couldn't establish connection to APM Server:\n%p", e.inspect

if the log level matches?

[firefart]

Ok the log_level never worked because it was overwritten by rubys loglevel. I now changed the gem a little bit and here is the stacktrace:

E, [2020-01-05T01:35:42.364893 #55] ERROR -- : [ElasticAPM] Couldn't establish connection to APM Server:
#<FrozenError: can't modify frozen String: "">
E, [2020-01-05T01:35:42.365114 #55] ERROR -- : [ElasticAPM] Traceback (most recent call last):
        5: from /usr/local/bundle/ruby/2.7.0/bundler/gems/apm-agent-ruby-997a01f1dc75/lib/elastic_apm/transport/connection/http.rb:92:in `block in open_request_in_thread'
        4: from /usr/local/bundle/ruby/2.7.0/bundler/gems/apm-agent-ruby-997a01f1dc75/lib/elastic_apm/transport/connection/http.rb:32:in `post'
        3: from /usr/local/bundle/ruby/2.7.0/bundler/gems/apm-agent-ruby-997a01f1dc75/lib/elastic_apm/transport/connection/http.rb:46:in `request'
        2: from /usr/local/bundle/ruby/2.7.0/gems/http-4.2.0/lib/http/response.rb:94:in `flush'
        1: from /usr/local/bundle/ruby/2.7.0/gems/http-4.2.0/lib/http/response/body.rb:52:in `to_s'
/usr/local/bundle/ruby/2.7.0/gems/http-4.2.0/lib/http/response/body.rb:52:in `force_encoding': can't modify frozen String: "" (FrozenError)

[firefart]

Looks like this error is caused by the http gem: httprb/http#582

[mikker]

Thanks for looking into it. We'll have to wait for the Http.rb team to fix it unless you want to run with their master.

[firefart]

A new version of the http gem (4.3.0) was released to fix this issue.