$ apt-get install librdkafka1   
Reading package lists... Done
Building dependency tree       
Reading state information... Done
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:

The following packages have unmet dependencies:
 librdkafka1 : Depends: libssl1.0.0 (>= 1.0.0) but it is not installable
E: Unable to correct problems, you have held broken packages.

root@5a5ed5d6a9d9:/# apt install librdkafka1
Reading package lists... Done
Building dependency tree       
Reading state information... Done
The following additional packages will be installed:
  libsasl2-2 libsasl2-modules libsasl2-modules-db libssl1.1
Suggested packages:
  libsasl2-modules-gssapi-mit | libsasl2-modules-gssapi-heimdal libsasl2-modules-ldap libsasl2-modules-otp libsasl2-modules-sql
The following NEW packages will be installed:
  librdkafka1 libsasl2-2 libsasl2-modules libsasl2-modules-db libssl1.1
0 upgraded, 5 newly installed, 0 to remove and 0 not upgraded.
Need to get 1854 kB of archives.
After this operation, 4834 kB of additional disk space will be used.
Do you want to continue? [Y/n] y
Get:5 http://deb.debian.org/debian stretch/main amd64 librdkafka1 amd64 0.9.3-1 [221 kB]
Get:1 http://security-cdn.debian.org/debian-security stretch/updates/main amd64 libssl1.1 amd64 1.1.0l-1~deb9u1 [1358 kB]
Get:2 http://security-cdn.debian.org/debian-security stretch/updates/main amd64 libsasl2-modules-db amd64 2.1.27~101-g0780600+dfsg-3+deb9u1 [68.4 kB]
Get:3 http://security-cdn.debian.org/debian-security stretch/updates/main amd64 libsasl2-2 amd64 2.1.27~101-g0780600+dfsg-3+deb9u1 [105 kB]
Get:4 http://security-cdn.debian.org/debian-security stretch/updates/main amd64 libsasl2-modules amd64 2.1.27~101-g0780600+dfsg-3+deb9u1 [102 kB]
Fetched 1854 kB in 0s (2397 kB/s)     
debconf: delaying package configuration, since apt-utils is not installed
Selecting previously unselected package libssl1.1:amd64.
(Reading database ... 6500 files and directories currently installed.)
Preparing to unpack .../libssl1.1_1.1.0l-1~deb9u1_amd64.deb ...
Unpacking libssl1.1:amd64 (1.1.0l-1~deb9u1) ...
Selecting previously unselected package libsasl2-modules-db:amd64.
Preparing to unpack .../libsasl2-modules-db_2.1.27~101-g0780600+dfsg-3+deb9u1_amd64.deb ...
Unpacking libsasl2-modules-db:amd64 (2.1.27~101-g0780600+dfsg-3+deb9u1) ...
Selecting previously unselected package libsasl2-2:amd64.
Preparing to unpack .../libsasl2-2_2.1.27~101-g0780600+dfsg-3+deb9u1_amd64.deb ...
Unpacking libsasl2-2:amd64 (2.1.27~101-g0780600+dfsg-3+deb9u1) ...
Selecting previously unselected package librdkafka1:amd64.
Preparing to unpack .../librdkafka1_0.9.3-1_amd64.deb ...
Unpacking librdkafka1:amd64 (0.9.3-1) ...
Selecting previously unselected package libsasl2-modules:amd64.
Preparing to unpack .../libsasl2-modules_2.1.27~101-g0780600+dfsg-3+deb9u1_amd64.deb ...
Unpacking libsasl2-modules:amd64 (2.1.27~101-g0780600+dfsg-3+deb9u1) ...
Setting up libsasl2-modules-db:amd64 (2.1.27~101-g0780600+dfsg-3+deb9u1) ...
Setting up libsasl2-2:amd64 (2.1.27~101-g0780600+dfsg-3+deb9u1) ...
Processing triggers for libc-bin (2.24-11+deb9u4) ...
Setting up libssl1.1:amd64 (1.1.0l-1~deb9u1) ...
debconf: unable to initialize frontend: Dialog
debconf: (No usable dialog-like program is installed, so the dialog based frontend cannot be used. at /usr/share/perl5/Debconf/FrontEnd/Dialog.pm line 76.)
debconf: falling back to frontend: Readline
debconf: unable to initialize frontend: Readline
debconf: (Can't locate Term/ReadLine.pm in @INC (you may need to install the Term::ReadLine module) (@INC contains: /etc/perl /usr/local/lib/x86_64-linux-gnu/perl/5.24.1 /usr/local/share/perl/5.24.1 /usr/lib/x86_64-linux-gnu/perl5/5.24 /usr/share/perl5 /usr/lib/x86_64-linux-gnu/perl/5.24 /usr/share/perl/5.24 /usr/local/lib/site_perl /usr/lib/x86_64-linux-gnu/perl-base .) at /usr/share/perl5/Debconf/FrontEnd/Readline.pm line 7.)
debconf: falling back to frontend: Teletype
Setting up libsasl2-modules:amd64 (2.1.27~101-g0780600+dfsg-3+deb9u1) ...
Setting up librdkafka1:amd64 (0.9.3-1) ...
Processing triggers for libc-bin (2.24-11+deb9u4) ...
root@5a5ed5d6a9d9:/#

root@5a5ed5d6a9d9:/# dpkg -l | grep ssl
ii  libssl1.1:amd64           1.1.0l-1~deb9u1                   amd64        Secure Sockets Layer toolkit - shared libraries
root@5a5ed5d6a9d9:/# dpkg -l | grep kafka
ii  librdkafka1:amd64         0.9.3-1                           amd64        library implementing the Apache Kafka protocol
root@5a5ed5d6a9d9:/#